I changed from McAfee to Norton about 4 years ago and have just updated to the 2003 versions of NAV and Norton Firewall. Some people report problems with Norton. I've had no problems at all though it does take time to configure properly to suite your system but once set up I find it excellent. The hand books which come with the CD's are easy to understand. I don't use N System Works.
Others on this forum will say go for the free AVG system. I think you pays your money or not as the case may be.