Nifft is correct about the Lightside/Darkside issue being more than just flavor. I am playing in a Darkside campagin right now and the guy who is playing the Dark force adept has used Force Lightning all of two times in ten sessions, and each time he cleaned house. I shudder to think of the damage he could do if he was using those abilities on a regular basis. He has been trying to keep the Darkside points under control but I found out that he is up to thirteen points now and starting to feel nervous about making those Fort saves. Another team member is already starting to make plans for the day when the Dark Adept totally looses control and tries to kill us all. So yeah, Darkside points matter.
But I will go beyond even that. Darkside points or no, the Jedi classes rock. SW is a universe where everybody walks around with one handed ranged weapons that do more damage than a greatsword and a Jedi can _still_ take on all comers. Which is right and just and as it should be. Jedi should be uber, Jedi should kick @$$
In the SW universe.
In any other setting they will be overpowered. I mean just look at the Jedi Guardian, he gets: Fighters BAB and Hit Die, three good saves, the second best defense bonus, four skill points per level, and enough bonus feats and special abilities to make even a monk jealous.
I don't think that you can simply do a straight conversion of the Jedi classes into a conventional D&D setting and call it balanced.
However, with that being said. I think that you could use the SW system of force powers as a good template on which to base an alternate psi system. To wit: take a feat to make an exclusive skill a class skill (can't get the skill on a class skill list, only by taking the feat) then spend vitality/power points/whatever to activate the skill and your skill check determines what kind of results/how effective the power is. You would have to start from scratch designing the skills and balancing them (the force skills being, again, _really_ powerfull) but it would probably work.
Or you might want to wait until the B5 game comes out as I hear that they will be handling Tep powers in a similar manner.
And just so you don't get mad that nobody is helping you answer your question: if you want a psion to have a lightsaber just say that, as a class ability, his psi crystal can produce a blade of energy with the stats of a lightsaber and he can deflect arrows and do all the cool Jedi lightsaber things with it. You have just handed him the most powerfull meele weapon in the game but as the DM I'm sure you can balance it