I gave Grisoft AVG Free Edition a test run lasting a couple of months on one of my Vista PCs. But, it just wasn't working out. It had some kind of weird interaction with Vista's own security mechanisms that kept creating a condition where an alternate display window of some kind was created where the virus update process kept getting stuck. So, I uninstalled AVG this evening and replaced it with the for-fee ESET NOD32 anti-virus product a try because I keep hearing about on Leo LaPorte's various shows ^-^ :-) and, well, ESET has a great deal for people awarded the Microsoft Most Valuable Professional (MVP) designation. I'm also still trying the Avast! 4 Free Edition on a notebook running Windows Vista. That is working out pretty well so far. If you know of other good freeware or Open Source anti-virus products for me to try out, please let me know.