i asked my boyfriend, and he said you should be able to reinstall right over the top, by using the original xp disc. you wont have to reformat the drive. you can avoid losing your files by using Norton Ghost. you might lose some software in the reinstall though. the boyfried says Norton Ghost will help protect your files from damage from the reinstallation of xp.
(i hope this makes sense to you, as it makes none to me, lol.)