Of course a Mac needs Anti-Virus
how else are you going to sanitize your buddies' PC's ? By far the easiest way to begin cleanup on an "owned" PC (of which there seem to be an awful lot these days) is to pull the hard drive, plug it into an external drive adapter, mount it on the Mac, and run ClamXav on it. I am not a PC repair professional, but I've done this three times in just the last week for friends and family whose PC's have digressed to near uselessness. Follow that up with a regimen of a decent (AVG or Avast!) AV package, a good Anti-Spyware (Spybot S&D or Spyware Assassin) and CCleaner on the PC and a few lessons for the owner and it has a chance of getting and staying clean and sober until next week at least.