If you are going to reinstall, disconnect your ethernet cable prior reformatting. (I like to wipe out the partition too) XP install will let you do both things during install (read the install screens carefully)

Make sure you have the latest version of your antivirus burned to a backup of some sort.
After the reinstall, install your antivirus, scan your system, activate the Win XP firewall, then plug your network cable back in and get all those updates from MS update site.