Well on my desktop we have avg free, half the time it won't put a virus is the vault, but instead makes you find it. And the automatic scan gets annyoying, if you leave your comp on at night, set it to run the test then, durig the day will chew up Alot of Ram, atleast for me.
AntiVir is ok, but the program was originally coded in German, and the English translated version isn't that great because you have a hard time understanding the menus.