I use the Microsoft Security Essentials (MSE). Seems to be fine here and has even caught a few viruses. It is more than anti-virus. Check Microsoft's web site for more. The default settings of scanning all file activity can be a nuisance when installing a big set of RealTracks but after they are there, no problem. This can be turned off if you're comfortable with it.

For gigs, I always disable my network adapters and MSE. I don't want the laptop to hiccup.

R