Account Settings have dissapeared after a system restore?

On my boyfriends main computer he was trying to delete the Genuine Advantage nag screen...being dsylexic he misread some things and ended up deleting one of the registry keys that allowed us to log in.
We followed the instructions set out here:
http://support.microsoft.com/kb/307545

Apon logging back into windows, all the settings, desktop folders and backgrounds had dissapeared and everything had been uninstalled, even the drivers for sound, graphics etc.
Everything in Documents and Settings is there, it's just that the username is not accessible.

Is there any reason for this and is it possible to get the old settings back or will we have to completely reinstall all the programs and drivers again?

 

I forgot to mention he uses Windows XP.