Seriously dude, after the second time you should have removed their admin or power user rights and given them a standard user account. Then install a decent antivirus that you can prevent them from changing the settings on and force daily virus/malware scans. Also, once the account is setup the way they like it, login as an admin and create a backup of their profile... or use any number of free backup solutions to create nightly backups and/or create nightly/daily restore points.
I hate to tell you this, but knowing what you know about how they use their computer, it's YOUR fault that they keep having this problem. 99% of the time you can prevent bad users from creating these problems or at least make the recovery a heck of a lot easier on yourself.
Buy a sysadmin for dummies book or something, learn a little about backups and malware/virus prevention. Learn to tell your users that it's for their own good(as well as yours). And if they don't like it, tell them to ask somebody else for help(a little harder with family, but still VERY effective to get your point accross).
Start chasing these guys down and giving them 10 years with no chance for parole... or better yet, look the other way when a mob hunts them down and breaks their knees...
Don't give him a choice, take everything AND put him in jail...
He has not acquired a fortune; the fortune has acquired him. -- Bion