The hardest thing about testing Windows Vista Beta 2 is not having a reliable antivirus solution that will watch your back. A little while ago Microsoft released a patch so that Symantec Antivirus 10.0.1.622 would work with Beta 2, and now they are doing the same thing for the free version of AVG.
I have installed the Free AVG on a countless number of computers for people and I have never heard of any problems with it. The greatest part is that I never have to worry about the subscription expiring which could result in an infected computer. They also offer a professional version that has a few more bells and whistles like a firewall. If you are just looking for a good antivirus solution then the free version should do you just fine.
Before you head over to download Free AVG you will need to perform a Windows Update to get the necessary patch because without it the antivirus will not function correctly. I am very impressed that Microsoft has been releasing patches to fix some of these antivirus programs especially since they have their own antivirus, called OneCare, to offer.