uhm , there is one thing good about a software firewall , is that if it's configured correctly it can alert you of unwanted outbound connections.
Oh as for NAV, I recently fixed a PC for a friend it was running slow. I assumed that because he had an updated NAV on his machine he was ok for viruses. So I cleaned up his tasks , ran CCleaner and Spybot and cleaned up the PC and it was still running slow. So since he only had 50 days left of his Symantec license , I uninstalled NAV and set him up on Avast. When Avast ran it's boot-time scan we found 10+ viruses which Avast proceeded to remove, both from his login and his restore points. Now his machine works OK ( I still think it needs a format and reinstall , since it's an old WinXP install on a laptop ).
NAV will never see the hard drive of a machine I own, ever. Nor will I reccomend it to anyone.