NAV provides a good firewall and an up-to-date definitions database, and if you get used to it, it's only intrusive when it needs to be. I dislike ESET, my friend was using it with up-to-date defs and he still had a load of viruses. Zone Alarm is basic security, but uses a lot of cluttering to make it seem as if it's good. AVG.. Well.. I suppose it's good if you're on the welfare or you don't know about handy little torrents. I managed to crack a 12 year licence of NAV on all my computers, but I couldn't do it recently for my friend, so you might find some trouble getting around their licences. As far as resources go, NAV uses about as much as any other firewall/av combo.