As far as I know, Windows XP doesn't have a reset utility unless you are lucky enough to have the restore point the closest to the install. you could also do a complete system clean-up. Log first in the administrator account to delete all other users. I'd use then "Glary Utilities" to delete/uninstall all installed unwanted programs and/or updates. only the listed ones sadly. Then use "registry first aid" or another registry scanner to clean up all the junk left in the registry. and finally, "Raxco perfect disk" to completely defragment the hard drive. Once done, reinstall your own softwares (anti-virus/spyware cleaner, etc...) and create the new users. It won't be as a newly fresh installed windows, but it should do the job.