Some have said that P5 runs better on W2k than XP. XP is a bit more flexible for games and such, so if you have a lot of programs that liked 98 and didn't like NT, you'd be better off with XP. On the other hand, I think W2k is a little less of a resource hog, but I'm not entirely sure. W2k and XP are about the same as virus catchers.