Is there an automatic way to keep nuisanace files off of my PC?

I am running McAfee Security Center for virus scanning. I'm connected to a router which allows me to share a cable modem and act as a hardware firewall. I tend to run Adaware every day or two and ALWAYS find garbage on my machine. It feels like a constant, on-going battle that I can't win. Are there tools I should be using that I'm not?

My daughters computer is worse although I think because she is a heavy user of AIM, all kinds of junk gets loaded on her machine to the point where it slows to an absolute crawl. Running MSConfig and looking at the Startup tab shows all the junk that's loaded. Unchecking the check boxes and restarting helps, but how can I prevent that stuff from loading in the first place?

I know several people that have been totally turned off from using a computer and browsing the net because this junk is out of control and is way too frustrating for the casual surfer.

Any advice? thanks