Windows ME - system restore How?

OK, here is my sob story. You know how family and freinds always call you with their computer problems. Well, my mother-in-law, who lives 2000 miles away, disoverd her windows ME system was infected with a virus. Over the phone I walked her through a Norton Virus scan. Sure enough 38 files were infected. Mostly the Klez virus. However there was one file in \windows\system or \windows\system32 that was infected. Unfortunately she could not tell me the name. NAV could not repair it. So the only choice was delete. Now the system is having some problems and NAV itself is acting up also. The system boots and works for the most part. But when trying to run install shield to re-install NAV she is getting a blue screen od death. I am thinking there must be a way to recover just the system file(s) lost without a total reinstall of the OS. Any suggestions? I have seen mentioned here in Q&A about system restore utility in ME. Is there such a utility and where might it be located?