I have the same exact rig as you for the most part. 6800 gt athlon 2600+ dual chan 1 gig ram. I tested 2000 vs xp when xp was on SP1 on quake 3 giants ut2003 on my old comp. Win2k had better fps on both of these games.. I have seen people having problems with windows xp for certain stability issues. I have not recently tesed 2000 vs xp on my new system. I would assume xp is still shit, it sorta seems like a newb os. But i would like to see benchmarks on a site or something cuz whenever i ask people what is better they say that xp is because its newer. When i tested them head to head awhile back 2000 won, so unless sp2 brought it up in the fps department than 2000 is a better os for gaming and stability.