there isn't any real reason why you should want to install xp to play games. vista is capable of playing most games, if your worried about frame rates, there is little difference, you might lose 1-2
frames a second. the most important thing is to upgrade memory. if a game wants 1 gig on xp, then supply 2gig. most people find 3gig, improves things further still. with vista 64 ...