Psionics in its entirety was redone from 3.0 to 3.5 - not just the psychic warrior The only thing that stayed the same was "there's a class named psion and a class named psychic warrior and they manifest powers" - just about everything else about the system changed, including power point progressions, number of powers known, the power mechanics, class features, etc, etc.
Here's a List. Note that most of these can be safely ignored and have little (if any) noticeable impact on the game. I've really only found those changes in the Official Core Book Update to be of much real consequence (to wit, I still use many D&D 3.0 rule books with 3.5 when I play).
[Edit: I missed the post by Abraxas. Sorry for repeating some of it.]