I switched from Norton to Zone Alarm two years ago, I now have ZA 2006. Norton was too much of a resource grabber and not too user friendly. The full version of the Zone Alarm Security Suite is much easyer on the system load. With anti-virus, firewall and anti-spyware built in. Not too expensive for the full licence, about £25.00 on Amazon at present.
http://www.pcmag.com/article2/0,1895,1891760,00.asp