This may help

http://www.dslreports.com/forum/r21915664-AntiVirus-Poll-2009

http://www.dslreports.com/forum/r19739894-AntiVirus-Poll-2008

I've had great luck with freeware AV apps
AVG comes to mind first in that regard
http://free.avg.com/download-avg-anti-virus-free-edition

Last time I used Norton ( a few years ago?)
it was so bloated it felt like I was pulling another entire
operating system through the CPU, etc.