You might also try Avast! Home Edition.
It is free, but you need to register it, and get a darn serial, like AVG, but it has many more features than avg, such as P2P monitor, IM monitor, Internet Mail, POP/IMAP/SMTP monitor, network monitor.
I have used it for a few months and have loved it.
It even detected a few viruses that were saved to a shared drive on a server, from a client that had it mapped. :)
www.avast.com
And hey, it even talks to you!
"Virus Database has been updated!"
or [Submarine Sounds] Virus has been detected! [\Submarine Sounds]