A friend of mine have a win XP system which is infected with virus and can't seem to be cleaned by Norton (don't ask me how they manage to get it infested in the first place). I don't know if they've got NTFS, but from what I remember, if they have NTFS, I can't get in with dos to do a scan. I know there's KNOPPIX which I can put on a CD and boot as an OS which can then mount the NTFS partition, but I'll need to know A) What's a good linux based virus scanner that'd work with Knoppix and B) how would I come about installing it. If anyone knows how to do this, please shed some lights!
If it's XP, to do a proper, thorough scan the computer first has to have system restore turned off (right click My Computer, click Properties, click the System Restore tab and put a check in the "Turn off System Restore on all drives" box). Then reboot in Safe Mode. Next, run a full manual scan. This should mean Norton is able to either quarantine the viruses or you'll be able to manually delete the infected files once the scan is complete.
When it's done, reboot normally, run another full scan (just to be on the safe side), and when that shows up as clear re-enable System Restore.
I know this doesn't really answer the main question, but it's how I de-virused my desktop computer the other night. Clean as a whistle now.