I agree with jjans - AVG is great. I usually go the AVG, ZoneAlarm, AdAware and SpyBot S&D route for Windows-based PCs, as well as using Firefox and Thunderbird for browsing and email.
I'd avoid any of the Norton utilities like the plague. They're slow and bloated and cause too many conflicts with other applications. I can't imagine why any home user would go with a Norton product when the likes of AVG are available for free.
And unfortunately, lots of ADSL modems are USB-based and have no internal NAT. Even with a NAT-based solution, I'd still install something like ZoneAlarm for home PCs or the paid-for AVG+firewall combo for computers in small business environments.
Or just use Linux! Ubuntu is getting better and better, though I appreciate there are still Windows-specific applications that don't run well on WINE.
-Ali
