I have three different "paid" anti-virus programs running on my 3 Vista computers here. All work well.
NOD32 v 2.7 - smallest footprint and fast, no firewall. Nice product & recommended highly.
Kaspersky Internet Security - Very strick and works well but doesn't play nice with the on-board RAID1 controller on my Intel 965 board. Great on a single drive system. Needs manually configured for a home network.
Trend Micro Internet Security Suite.- The strictest of them all and takes some time to configure fully.
I have also used the free McAfee programs available for Comcast users. They seem to work well also.
I agree with linney above. If you're a savvy user and stay to business sites, etc., free AVG works very, very well.
My wife and daughters computers have the security suites on them with high security settings to save them from themselves. I use NOD32 on my office PC, because I hope I know not to click on the flashing box that says I just won a million dollars!
Hope this helps someone...
Jeff