I have a confession: I've been running my Windows XP system sans anti-virus software for many months. Crazy? Perhaps, but I consider spyware a much bigger threat these days, and I'm well-protected against it. I also detest the wallet-draining performance anchor that is anti-virus software.
How's that for a rousing recommendation of Norton AntiVirus 2008! Today only, you can get it from Fry's for $0 after a $50 mail-in rebate. This is the 3-user edition, meaning you can install it on up to three PCs, and it also includes anti-spyware protection and rootkit detection. Plus, Symantec promises much faster scanning and operation in this version, though I have my doubts. Of course, it's free, so if it bogs down your system, you can always uninstall it, no harm done.
Norton AntiVirus 2008 requires Windows XP or Vista. Frys.com requires blinders: It has to be the ugliest online store I've ever seen.