Since we're tossing stuff out there... a-squared Free - Free of charge Anti-Virus, Anti-Trojan, Anti-Spyware, Anti-Dialer and Anti-Worm Software - Freeware!
This is a unique product in that it uses 0 system resources. It does not run in the background, it runs on demand and it finds stuff the background scanners don't.
There is no
reason that anyone needs full time anti-virus and security running in the background on their computers. If you scan your executable downloads, check your email attachements (which a-squared does by right clicking the file) you're not going to get virused.
For firewall and security, Windows native firewall does as good a job as any. If you are running in a LAN with a router that has a firewall, you can even disable the windows one with mo problems at all.
I've been using computers and bouncing around the internet for nearly 25 years and I've only once gotten nailed by a virus... and that was my own silly fault, clicking on unknown links in email spam.
Use some common sense, scan your system weekly, and you've got all the protection you need.