Confirmed that the initial name entered in Windows is in the Registry. On my XP Home laptop, going into help found a Windows Knowledgebase article that describes changing the registry to change that name.
Webroot's Window Washer would probably take care of everything else, but you would probably have to delete the users. Windows does warn that if you delete a user, or someone other that the user themselves changes a user password, that users files are not retrievable. (Some hacker somewhere probably has a package to do it).
You could probably wipe the disc and reinstall XP using the Certificate number on the bottom of the laptop, but drivers might be a problem, depending on how old the laptop is. If you had access to an XP SP2 disc, and your laptop predated 2004, the drivers might be in XP SP2. Or you could just let the generic drivers load, hook up to the internet, and let the system look for better drivers.
Moral of the stiuation - when you get you new laptop, put the DVD's in a safe place and make copies. If Toshiba is like HP, you will have to burn your own originals. Then make a set of copies. You can only burn one set. If your laptop has never had a CD burned from the orginal installation, you might still be able to do that, but it would take info from someone that knows Toshiba.