I recently started using avira antivir, the free personal edition. One thing i found annoying was everytime it would update the virus definitions, it would pop up an ad to buy the better edition. While searching on google, I found this page that explains how to block that pop up. Instead of c/p this info, i will give credit where it is due. So just go check out that link.
http://www.tipsfor.us/2007/08/15/make-avira-antivir-free-edition-more-usable/
The thing that this antivir is lacking is the scanning of incoming email. Most non-power users have free mail, ie, gmail or hotmail, so in my opinion, you dont need the email scanning option. This would be an issue if you use outlook / express; then I would recommend buying the better version or go for another great free product – AVG.