Ha. Yeah right. That's what you say. Antivirus is essential my friend. Especially if you go with a free one. Personally I used to use AVG, but now I like and recommend Avast.
I worked on one machine, maybe similar to arges86's friend's machine, an xp laptop, no antivirus ever installed in a few years from what I could tell. They just wanted a tuneup. No big deal. But I think I removed about 600 different things from that machine.
So even if malware is not causing noticeable trouble, if you are connecting to the web, I say antivirus is essential, especially when you can get antivirus for free. I use Avast for Antivirus in conjunction with this free firewall http://download.cnet.com/PC-Tools-Firewall-Plus-Free-Edition/3000-10435_4-10625321.html?tag=mncol
Seems to generally keep the system clean. Granted Windows does have built in firewall which is fine for most people, but nice thing on this one, you have to teach it. It seems decent at detecting if things are trying to go in or out of your pc to and from the web, and allows you to block or allow them. Using this combination, I've had relatively few issue*knock on wood*. But still stay away from unknown sites.