One little thing to remember, though, if you are installing XP overtop another WinBlows OS.
I know this may seem common sense, but I'll post anyway: make damn certain you uninstall OS-intensive things like Norton Utilities 2000 and such, which have a firm hand 'round the cojones of your OS. In my fervor to try out XP on my desktop, I pulled a Homer and forgot. It was like putting a prom dress on a pig, same amount of heads/limbs but not really a good fit (and where *does* the tail go?). You can theoretically uninstall XP and go back to your previous OS, then uninstall all pesky interlopers, then reinstall XP, *then* of course all your new XP device drivers.
That's if it lets you; mine did not, and I had to reformat the drive (though XP does offer you that lovely NTFS).
And of course, if you installed any software since installing XP, *especially* XP-specific software (Tweak XP comes to mind), you'll do well to uninstall them BEFORE you uninstall XP, so you can then go back to your original OS...simply, it's gotta be easier to do it right the first time.