First and foremost, since you already have Norton Antivirus installed (part of the Norton Suite) you should not install another AV product alongside it. If you want to install a different AV, Norton AV will have to be removed first. Running two AV products can cause instability, indeed most AV products won't install if they detect you already have one.
I should point out also that, apart from Norton AV receiving very low scores in recent virus-detection tests, it is also infamous for using high levels of system resources, and this also applies to Norton Firewall. I've used them both (provided free by my ISP) yet despite being free I've had to remove them and buy my own alternatives. Norton is just too much of a memory glutton.
So perhaps your decision as to whether to get rid of Norton has now been made easier? Well, I can unhesitatingly recommend AVG Security Suite which uses only half the RAM that Norton uses yet consistently beats it on virus-detection. It also comprises a Firewall and anti-spyware component.
You can get AVG Security Suite here: http://www.grisoft.com
Edited by pip22, 21 April 2007 - 10:21 AM.