I previously used an all-in-one Norton security package, but my subscription ran out and I didn't want to keep paying for virus definition downloads and software upgrades. I decided to do some research. Here's the best free solution I could find:
Firewall: Zone Alarm Free Firewall
Anti-Virus: Microsoft Security Essentials
Zone Alarm is a bit aggressive and shows a lot of pop ups at first, so I don't recommend it for non power users. However, I'd rather have a firewall that's aggressive as opposed to soft. FYI, the built in Windows XP firewall DOES NOT block any outbound traffic, only inbound. This means that it can stop incoming attacks, but can't protect against malware that's already on your system and is trying to dial out.
MS Security Essentials is a new thing that kind of slid in under the radar, but is being reviewed favorably. It seems leaps and bounds above the other free packages, but is probably not quite as good as the expensive third-party stuff. Still, it's free, and seems clean.
I realize that this post seems like an advert, but I honestly wanted to share my data mining results with you guys so that you can all browse porn safely and without fear.