The Jedi are a part of the Galactic Republic and will be a playable class, as an alternate to the Sith Warrior. As such, it would be beneficial to understand how and why the Jedi Order operates, to better anticipate what possibilities Bioware might throw at you. Without a further ado, let's get started.
Founding of the Jedi Order

The above picture shows the rebuilt Jedi Temple on Tython. This became the new focal point of the order after the Jedi fled their temple on Coruscant because of its destruction. This is important because the earliest records of a Jedi Order shows that the organization was originally founded on here around 25,783 BBY (Before the Battle of Yavin), several hundred years before the founding of the Galactic Republic.
Wise and powerful people came together on Tython to discuss the Ashla, or light side of the Force. However, many became seduced by the Bogan, or dark side of the Force, and tried to take control. This tale repeats itself throughout Jedi history and is still relevant when The Old Republic's storyline takes place. It is not unlikely that you might face those Jedi, whom you previously took quests from, as a few of them may become seduced by the dark side of the Force; even your character might not be able to escape its alluring grasp.
The Jedi Code
The Jedi Code exists as a set of guidelines for all Jedi to strive to imitate. This is the code that each Jedi uses as a constructive basis for all their decisions. Because of this, it is greatly important for all Jedi to understand what it means. The original code was refined by Master Odan-Urr and is still in use by the time The Old Republic takes place.
Lets examine each tenet of the code in greater detail.
There is no emotion, there is peace. This tenet says that a Jedi must not be ruled by their emotions. Emotions are not to be overcome or denied, but rather understood and dealt with. Unless a Jedi can confront his thoughts and feelings, he will never achieve peace.
There is no ignorance, there is knowledge. This tenet says that knowledge can be found in any circumstance and should not be ignored because the source doesn't fit with your viewpoint. Even the foolish can be wise, so a Jedi must use every opportunity to learn and grow.
There is no passion, there is serenity. This tenet says that a Jedi can not allow passion to cloud their judgment lest they act rashly and lose objectivity, therefore inadvertently allowing themselves to walk towards the dark side of the Force.
There is no chaos, there is harmony. This tenet says that everything happens for a reason and that everything is connected through the Force. Failure, disappointment, and disagreement are all apart of life, so they should be used as a learning experience. This allows for a balanced, objective, and realistic point of view, which is very important for a Jedi.
There is no death, there is the Force. This tenet says that a Jedi must always be ready for death, and not obsess or be ruled by it. A Jedi must understand that life is a cycle and without death, life could not exist. Death is a transitory state for any living being and is not truly an end to life, but merely the beginning of the next stage of "life's" journey.
Jedi Hierarchy

The above picture shows a Jedi Master, Knight, and Padawan. The hierarchy of the Jedi Order is important to understand because when you create your character, you will probably start as initiate a or padawan. Then, through time, you will probably progress through the ranks. So, if you understand the hierarchy, you can better understand what will be expected of you as you quest.
Most Jedi start out as a Jedi Initiate. A Jedi Initiate is a force-sensitive child who was removed from their family at a very young age to be taught by older Jedi. Think of them as students. After a certain period of schooling a Jedi initiate progresses to a Padawan when a Master or Knight chose to take them as an apprentice. They traditionally wear a long braid of hair behind their right ear to show their rank.
A Padawan will normally only progress to a Knight after they completed "the trials." These trials included, but were not limited to:
The Trial of Flesh: A Jedi must overcome great physical pain, hardship, or loss.
The Trial of Courage: A Jedi must fight courageously in battle, complete missions with a low chance of survival, or defeat a superior enemy.
The Trial of Skill: A Jedi must duel with an adversary or display particular skill in the Force.
The Trial of the Spirit: A Jedi must look inward in an attempt to make a self-discovery.
Only a Jedi Knight, who has shown a great understanding of the Force and managed to instruct a Padawan to the rank of Knight themselves, can become a Master. This title can also be achieved through the performance of extraordinary deeds. Of these Masters, only a very few ever become Councilors. A Jedi Councilor was one whom serves on the Jedi Council. The Council is made up of twelve masters, five of them with lifelong terms, four as long-term, and three limited-term.Very, very few Jedi become Jedi Grand Masters.

For those of you who are interested in reading more about the Jedi, I suggest reading this article on Wookieepedia.
That was the Jedi Order in a nutshell, though I barely scratched the surface on the volumes of information that is available for anyone who is willing to read it all. This information is relevant because Star Wars: The Old Republic will not only use, but build upon the preconceived notions of previous canon. These notions will allow all of you who chose to play a Jedi to play one to the best of your ability.

The above picture shows the rebuilt Jedi Temple on Tython. This became the new focal point of the order after the Jedi fled their temple on Coruscant because of its destruction. This is important because the earliest records of a Jedi Order shows that the organization was originally founded on here around 25,783 BBY (Before the Battle of Yavin), several hundred years before the founding of the Galactic Republic.
Wise and powerful people came together on Tython to discuss the Ashla, or light side of the Force. However, many became seduced by the Bogan, or dark side of the Force, and tried to take control. This tale repeats itself throughout Jedi history and is still relevant when The Old Republic's storyline takes place. It is not unlikely that you might face those Jedi, whom you previously took quests from, as a few of them may become seduced by the dark side of the Force; even your character might not be able to escape its alluring grasp.
The Jedi Code exists as a set of guidelines for all Jedi to strive to imitate. This is the code that each Jedi uses as a constructive basis for all their decisions. Because of this, it is greatly important for all Jedi to understand what it means. The original code was refined by Master Odan-Urr and is still in use by the time The Old Republic takes place.
There is no emotion, there is peace. There is no ignorance, there is knowledge. There is no passion, there is serenity. There is no chaos, there is harmony. There is no death, there is the Force. - Jedi Code
Lets examine each tenet of the code in greater detail.
There is no emotion, there is peace. This tenet says that a Jedi must not be ruled by their emotions. Emotions are not to be overcome or denied, but rather understood and dealt with. Unless a Jedi can confront his thoughts and feelings, he will never achieve peace.
There is no ignorance, there is knowledge. This tenet says that knowledge can be found in any circumstance and should not be ignored because the source doesn't fit with your viewpoint. Even the foolish can be wise, so a Jedi must use every opportunity to learn and grow.
There is no passion, there is serenity. This tenet says that a Jedi can not allow passion to cloud their judgment lest they act rashly and lose objectivity, therefore inadvertently allowing themselves to walk towards the dark side of the Force.
There is no chaos, there is harmony. This tenet says that everything happens for a reason and that everything is connected through the Force. Failure, disappointment, and disagreement are all apart of life, so they should be used as a learning experience. This allows for a balanced, objective, and realistic point of view, which is very important for a Jedi.
There is no death, there is the Force. This tenet says that a Jedi must always be ready for death, and not obsess or be ruled by it. A Jedi must understand that life is a cycle and without death, life could not exist. Death is a transitory state for any living being and is not truly an end to life, but merely the beginning of the next stage of "life's" journey.
The above picture shows a Jedi Master, Knight, and Padawan. The hierarchy of the Jedi Order is important to understand because when you create your character, you will probably start as initiate a or padawan. Then, through time, you will probably progress through the ranks. So, if you understand the hierarchy, you can better understand what will be expected of you as you quest.
Most Jedi start out as a Jedi Initiate. A Jedi Initiate is a force-sensitive child who was removed from their family at a very young age to be taught by older Jedi. Think of them as students. After a certain period of schooling a Jedi initiate progresses to a Padawan when a Master or Knight chose to take them as an apprentice. They traditionally wear a long braid of hair behind their right ear to show their rank.
A Padawan will normally only progress to a Knight after they completed "the trials." These trials included, but were not limited to:
The Trial of Flesh: A Jedi must overcome great physical pain, hardship, or loss.
The Trial of Courage: A Jedi must fight courageously in battle, complete missions with a low chance of survival, or defeat a superior enemy.
The Trial of Skill: A Jedi must duel with an adversary or display particular skill in the Force.
The Trial of the Spirit: A Jedi must look inward in an attempt to make a self-discovery.
Only a Jedi Knight, who has shown a great understanding of the Force and managed to instruct a Padawan to the rank of Knight themselves, can become a Master. This title can also be achieved through the performance of extraordinary deeds. Of these Masters, only a very few ever become Councilors. A Jedi Councilor was one whom serves on the Jedi Council. The Council is made up of twelve masters, five of them with lifelong terms, four as long-term, and three limited-term.Very, very few Jedi become Jedi Grand Masters.

For those of you who are interested in reading more about the Jedi, I suggest reading this article on Wookieepedia.
That was the Jedi Order in a nutshell, though I barely scratched the surface on the volumes of information that is available for anyone who is willing to read it all. This information is relevant because Star Wars: The Old Republic will not only use, but build upon the preconceived notions of previous canon. These notions will allow all of you who chose to play a Jedi to play one to the best of your ability.
Comments
The Force is just a neutral tool. A hammer could be used to build a house or bash someone's head in. Its negative uses don't negate its use as a positive tool. I'm sure Force Lightning could be used to restart a heart if one used it positively. Likewise, Force Push could be used to push someone off a cliff to their death.
"You have failed your highness. I am a Jedi, like my Father before me."
I really hope they let us have more than one toon per server (i'm hoping at least 5). Both sides seem like they have so much to offer. It's really not just 2 sides of the same coin; they're def very different.
That is not evil, that is being a jerk. Evil would be taking the poverty and using it to manipulate the weak to your will. To steal lunch money is easy. To get them to be part of your private army, or spy on your enemy for a loaf of bread is where the real evil points start to rack up.
I'm planning on playing an Empire side class once the game is released, and hoping that there will be options to build my character based on principles and objectives, such as crippling the republic, seeking power, but at the same time not being some evil thug who goes around Coruscant stealing food from poor families just to earn dark side points. From what I've read so far, it seems as though those options will be available to me.