Wow, that takes me back.
The problem as I see it is that there aren't any perfect solutions once the machine is badly infected.
Trying to go after the problems you can see doesn't help long term since you'll miss a few, and they'll log on to an irc channel or something and download it all again.
Even an expert has real problems sorting out a seriously compromised installation, I really don't think there is any way that a novice has a hope no matter how much help is provided.
The real solution has to be stopping them from getting infected to start with - which really only takes a decent firewall and an understanding of what not to click on. However the latter is not going to happen anytime soon.
I'd advise never charging anyone for clearing crap off their PC. A couple of months down the line they'll have just as much crap, and now it's your fault.