To pay for Anti-Virus is not a smart thing to do. Norton is a slow pig too.
This proggy will do the job for you - for free. Turn off VDRB generation though when you install it - I find that part annoying.
http://www.avast.com/
-S
PS. Here is the link for downloading -
http://www.avast.com/eng/avast_4_home.html