I would suggest Zone Alarm as an alternative to Norton. The free version is terrific, it blocks everything and doesn't require a lot of system resources to run. The free version also lets you customize what programs you want to grant access to the internet. It's also updated frequently. The Zone Alarm Pro which costs money has a lot more functionality (individual blocking or opening of select ports, etc.) I use the free version and its passed every internet security site that checks for open ports and vulernabilities that I've been to.
I gave up on Symantec products after their Utilities 2002 fiasco. There's better and cheaper (can't beat free) alternatives out there for sure.