Files missing due to virus (Win95)

A friend is running Windows 95 and has recently learned that his computer is infected by a variety of viruses.

He is planning on refreshing his computer from the startup CDROM, but wants to disinfect the viruses first. On trying to install theanti-virus program, an exception comes up saying that necessary files are missing.

Is there a utility that checks to see if all of the files are on the computer that are required to run WINDOWS 95? He has a Windows 95 CDROM disk.