Quick Virus Question

I've always have run a tight ship so I very rarely get a virus, but I've got a client who has somehow managed to get some sort of mailer Trojan horse on their computer HOWEVER, Norton Antivirus has the virus isolated and ready for removal.

From the instruction sheet (I'm assuming they got it from Symantec), they updated Norton and did a full system scan.

The virus shouldn't do anything since Norton has it quaritined, correct?

Now, it may have injected values into the Registry (which is why they want me to do it as they don't know what the registry is, let alone know how to access it and delete values from it). I don't think this will be a problem since I can read the Symantec technical data sheets so the registry is not a problem.

Working on Linux a lot makes me glad I don't have to deal with viruses... man, Windows sucks...