Geez, I guess all the agreement with me from a lot of folks on this board whose opinion I respect shows JUST HOW BAD NORTON AV IS!
I thought I'd mention, in view of what else has been said, to offer a couple other experiences I've had. Avast, though a very good AV, didn't play well with some of the other software on my machine. YMMV. I had Avira AV for awhile and it let something through. Panda didn't play well with others, even worse problems with it than Avast, its support page is a PITA, and the support people don't communicate well in English. Kaspersky so far has been golden.
There is a free, slightly stripped down version of Kaspersky available here:
Active Virus Shield
Very informative thread!