in my experience 2k is more stable and less buggy than xp. the functionality is basicaly the same. xp has some better desktop-gfx and a more colorful design...not to forget media player 9 and 10 (but who really wants them?).
its a fact, that more users use xp than 2k. but thats because every pc is shipped with xp. i've never seen a dell-pc for example with 2k.
why is it, that you think that xp is better suited fo gaming than 2k? imo the basic functions are the same. look at the graphics-drivers from ati for example. they are the same for 2k and xp....
..but were getting wwaaaay off topic, aren't we?
p.s.: if youre happy with xp...no prob for me. but i had only bad experiences with that os.