First, and I'll probably get a lot of flames for this but, they should
really get Symantec Norton Anti-Virus. Much more user-friendly
and for the most part automatic and unnoticable. I have worked
on literally nearly a thousand virus infected computers and a great
majority of them had McAfee on them. But..apples and oranges.
First, they should remove the virus first and then install the anti-virus
to a clean (virus free) machine. Some strains of virus will actually
disrupt the install or affect it in some way.
They can download the virus remover from Symantec's site:
It's might be better to run the cleaner in safe mode. After it is clean,
that's when you want to install the anti-virus and definately update it.
You may find even more virii on the machine.
On a personal note, There is absolutely no reason that you should
not have anti-virus on your windows machine (I know).