Hi Gary,
I used to be training at GeekU's malware removal school but had to leave (about a week ago) during the last stage of my training because I wasn't able to fit it in with my studies (I'm currently at university). There's a few points I want to go over with your post:
Combofix
Everyone will warn you about the risks of it bricking your computer etc. but IMO this risk is non-existent, I don't know why people say this - I assume it's to warn non-trained users from using such a powerful tool. The term bricking is used very loosely on forums, personally I think the term should only be used when computers are completely broken beyond repair. The real risk, as I see it, is people using automated tools (like CF) and thinking the problem has gone. Rule 1 of malware removal is that a lack of symptoms doesn't mean a clean computer. CF may remove the visible traces of an infection, but there could be all sorts going on in the background. Without knowing how to read the logs, I can almost guarantee that every computer you've cleaned (excluding clean installs) in the past will have remnants of the infections still on them - these remnants may or may not be dangerous. It's when people use automated tools that they get lulled into a false sense of security. This is especially dangerous when the people you're helping are in a retirement home and may be less familiar with a computer.
Hitman Pro
This is widely known to cause a lot of problems (BSODs, errors booting Windows etc.) so I'd keep a wide berth from this.
Just have a look at a few threads where trained helpers are working:
Virus, Spyware, Malware Removal
Virus/Trojan/Spyware Help
There's a reason they all have to manually remove files and don't just throw automated tools around

Also, the Combofix tutorial is about 300 A4 pages long so there's a lot to know before you can use the tool properly.
It's great that you're helping people for free, but you've got to make sure you (and the people you're helping I guess) understand the risks of you doing so.
Tom