Virus

Hi,
I have a friend who’s pc has a virus that is attacking his system tray, norton antivirus IE and his system restore, so basically there is no way to get online to run virus fixes or to run a system restore. When and if we open the task manager there are a whole bunch of files running that we cannot quit. There are three .exe files that are always running that when we try to quit them it comes back with an error message that says something like it cannot quit important files. Any ideas on how to fix this anyone?
Thanks!