Norton Internet Security draining system resources

I have been struggling with low system resources from time-to-time and thought it might be my Quicken program or Internet Explorer because both of these applications seemed to show a serious drain on resources. However, through an inadvertent twist, I think I have discovered that it is Norton Internet Security that is the problem.

For some reason my NIS program was corrupted so I had to uninstall it and reinstall (I downloaded NIS 2004 from the Symantec website). While NIS was removed from my computer, my resource meter was consistently running at between 76-83% for the User even when I was on the internet (scary when I had no virus protection). As soon as I had it reinstalled - BOOM, the resources plummeted again when I was on the internet. Twice, it went into the red or completely out of view telling me to close some programs.

Can anyone help me with this problem - is it normal for NIS to drain the resources by 40-60%? Is there something I can do to prevent it from this drain - I know there are several items in the startup linked to NIS but I don't think I can get rid of any of them. Any help would be appreciated.