Even Norton 2008 is a serious resource hog. However, it was rebuilt from the ground up with Norton Internet Security 2009. According to THIS ARTICLE by Maximum PC, Norton Internet Security was one of the top AV they tested. If you're using anything earlier than this, I'd recommend upgrading.
Personal experience has shown me that anything older is a waste of a good system. I've removed Norton from 3 or 4 computers, installed Avira, and actually have seen a noticeable increase in response time.