You mean all.
A few steps to prevent virii:
1) Install FireFox. It helps, especially if you don't know what you're doing. It helps a lot more with spyware than with viruses, but the lack of ActiveX is indeed good.
2) Don't download anything that comes from a source you even THINK you can't trust. That includes sitehere.geocities.com sites.
3) Run SpyBot and AdAware every week, at least once. Spyware is a different entity altogether, but it CAN download malware, or virii to your computer.
4) Get a router. If you can't get a router, get ZoneAlarm personal edition. The free one.
5)
http://housecall.trendmicro.com your best friend. Ironically enough, though, it can only be used with IE right now.
Finally, don't fret over virii. Sure they're a pain in the ***, but there's nothing that really screws you over in any way. If nothing else I'd reformat if you can't fix it. That's a pain, but hey, it's better than having a virus on your system
Also, tell your dad that online gaming has no impact whatsoever on the system as far as virii go. In fact, it is infinitely safer than just browsing the intarweb.