Whatever you do, do not update Norton past 2003. After that, it will disable your internet connection and cripple your PC should you let the subscription expire. Downright evil sh*t man.
I use McAfee 6 on my main PC because it can be fully controlled and does not mess with the internet connection. I fully disable the on-demand scanner and only do a monthly scan. Stay away from McAfee 7 and up, they strayed from just making a good virus scanner into making bad software firewalls, like Norton.
On other machines I use AVG because it is efficient and free, though somewhat unweildy to fully disable the on-demand scanner.