Windows XP might require you to reactivate, but that's not a major problem at all. If you have a win98 startup disk, it has fdisk on it. If not, download it
here. If your hard drive is over 64Gb, you'll need the new fdisk which is available at the bottom of that page.
edit- With XP, just put the disk in and it will let you delete your old partition and reformat during installation.
-Kc2iLq