My guess is that computer will crawl at an unbearably slow pace with XP on it. For some reason, XP seems faster on 1Ghz+ computers, but slower on 1Ghz or below computer (not EXACTLY 1Ghz, but you get the idea). It makes better use of newer hardware, but it's still got more bloat than 2000 that slows down older machines.
My suggestion: use that box to try out linux. I suggest Fedora Core but leave off Gnome and use XFCE. Otherwise, Damn Small Linux with XFCE or Fluxbox would make that computer fly.