I'd suggest AVG or AVP (Kaspersky -
www.avp.ch)
I've used Kaspersky a lot, and works very well. Far better than Norton (IMO). At the moment I've got the windows box on Grisoft's until I can get another AVP licence.
I haven't really had a chance to test Grisoft yet. But one thing I've noticed is lots of features are disabled in the free version. Its those features you need when a virus is wiping out a system.