I'm not a fan of AVG, I dont think its updated promptly enough.
Ive always used Sophos, which is what several Govt IT systems use, but its obviosuly not free. Unfortunately Ive moved products due to it becomig unavailable to me from March this year.
My recommendation is Avast (
www.avast.com ), which is a comercial product for business use, but they offer it free to home users.
As its commercial, you get frequent and prompt online updates. Its also quite good for not hogging system resources (ie Norton), which is why I always liked Sophos.
As for a firewall....if you are running Windows XP Service Pack 2, the inbuilt firewall is perfectly adequate, especialy if its backed up by a routers inbuilt hardware firewall. It may not have all the bells and whistles of something like Zone Alarm, where you can see the logs of IPs hitting you, and become paranoid trying to find out what they all are, but it does the important thing, and thats protect you. Ive been running only this since SP2 came out, and at least 1 of my PC's is on 24/7 downloading, and ive never had any problems.