What is the best free antivirus for windows xp pro x64 eddition?

Avast seems to be one of a few antivirus applications out there that support the Windows xp pro x64 operating system, and it's free. Although you still need to find a compatible firewall. AVG is good and I think it also has a firewall. As an XP x64 user I have found Comodo Internet suite seems to run the best as far as resources and ease of use. It also has a built in firewall and is pretty much "plug and play" in that you basically install it and let it do its job. Everything from scanning to updates to firewall rules has already been done for you, but these are trivially easy to change from the Comodo control panel if you so desire.