I only had version 2526 of XP on my computer, there are some really good features with it, but i found it slowed down some things quite a bit. I did some really strange things with the CPU utilization, sometimes when there was nothing open, the CPU would sitt on 100% for a few minutes at a time, when you did try to open anything it would be slow. The most annoying thing with it was, when you drag across multiple files, eg to copy them, the would become unbearbaly slow, might be a bug with the version i had. The internet seemed incredibly slow too, some sites would take forever to open.
It also wouldn't let me put the latest divx codecs on the computer, the default media player wouldn't open any videos, the old media player which came with it would though. The new media player is crap anyway.
Oh, the drivers for a HP deskjet 640C which it installs are crap, but it won't let you put any better ones on, my HP scanner 4300C will not work with it at all, despite the fact that it picks it up as being plugged in, and with the drivers, nothing i could do would make it work.
I found 2000 to be better, i just reinstalled 2000 back on now everything works well again. I might XP back on when the retail version comes out.
BTW, my comp is
Athlon 750
Asus K7V
512M RAM
1 x 30G WD HDD, 1 x 20G WD HDD
TNT2 Ultra (my GTS is at the shop being replaced)