I run a D&D IRC channel, so maybe I can answer a few questions.
3.5 vs 3.0 Very basically 3.5 nerfed a bunch of spells ( primarily buff spells) and made rangers and dwarves VERY powerful. It also nerfed the sorcerer class, slightly boosted bards ( a good change IMO), improved the skill list, altered monster damage resistance significantly, and changed the spell focus and power attack feats and a number of popular prestige classes.
I don't like 3.5, but I play casters and the thing I liked best about 3.0 was that it had nice strong (but not crazy strong IMO) spellcasters.
If you want to look at the differences read the SRD ( Note that the srd isn't as "user friendly" as the players handbook, since it was writen for gme designers to reference)
http://www.opengamingfoundation.org/srd.html has the 3.0 srd and a link to the 3.5 as well.