Why not go to ETrust where you can get both Firewall and AV free for 1 year. The firewall is Zone alarm to all intents and purposes and the AV is excellent. I have been running the both now for about 6 months and I think that I will probably subscribe when my 12 months free are done. They are also compatible with SP2 and are recomended by Microsoft. In fact I got mine on a disc together with all the old updates for SP1 click here
Don't get ZoneAlarm with AntiVirus. It is a good program but I found it slowed my machine to a virtual standstill. Very resource hungry. However that's my opinion. If you do decide to use it get the free trial and see how it works on your machine.