Shell32.exe not found

Ok here is the problem one of my clients picked up a trojan and the antivirus got rid of the file shell32.exe that the trojan tried to put on the computer.Now here is the tricky part the trojan changed registry keys to point all exe’s to the shell32.exe to open programs. So now I cant open any programs with .exe extention even in safe mode.I could edit in command mode but I dont know what trojan got into the computer and what keys to delete. Any Ideas what I can do to rectify this problem??