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.
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For the future, I suggest you take an image of the HDD in it's 'clean' form - there are free disk imagers around. You can then go back to there any time you like, and it's a lot quicker than reinstalling Windows.
Windows does not come with any program to make what you ask a simple point and click thing, unless you have system restore.
The best fix anything Windows and Microsoft related that I've found so far is:
go to command prompt (run -> cmd)
type in: "format C:"
Soon everything will be better...
Get a copy of Linux.