Since you're committed to Windows, you should go with Vista. IT doesn't matter whether its better or not. XP will be increasingly out of date. The direction the windows OS has gone from 3.1, thru 98, XP and to Vista is a straight line. You've chosen to also go in that direction, so either you stop at XP and have increasing hardware incompatibility, and no forward progress, or you back up your decision and take Vista now, and each successive release they do.

So, why are you even asking? You've picked crap and the flavors of crap similar enough that the loss of utility of sticking with old crap outweights the fact hat the new crap, naturally, tastes worse.