I use Clam Win as its open source, anyone who works in security/crypto will tell you this is the only way to run safe and secure code.

NOD is very good but you have to pay for it, IMO you only need that amount of AV security if you have many people using your computer that will go opening all spam sent and going off to any part of the interweeb without using any sort of software firewall and anti spyware/malware blocking to keep software/websites in control.

A hardware firewall can only filter something from the outside from coming in, so if you run UPnP of have any sort of closed software on your computer it can let in or open any ports for anything to drive right thru the hardware firewall as well as being able to send any information home. Things like XP (which reports back in 12 different ways on your computer habits) 'phone home' to keep track on what you use the computer for, even Zone Alarm does this (just google zone alarm spyware) I dont know if that has been sorted as IMO there are many far better free firewalls out there that work much more than ZA does.

I dont run AV full time as I dont need it, I only scan downloads and dont go reading spam, or blindly following any link. A good software firewall is much more important than real time AV software IMO (and many others).