Keep your virus definitons up todate.
I have never install any Zone Alarm, Black Ice, Internet Security on my PC, and I have only had 1 time where i had a problem. And that was with BACKORFICE many years ago.
They only software i use to protect my OS is :-
* McAffee Virus Scan
* SpyBot S&D
* AdAware 6.0
* HiJack This
I am also behind a NetGear DG814, but that only has a MILD firewall.
IMHO, Internet Sercurity Software is some thing that the average home PC user does not need. I have more problems with Virus and Spyware (both personally and professionally) than I do with people trying to hacked in by some out side source.
How ever, this is also dependant on the type of internet user. I guess I am the type of internet user that does not attract this sort of attension in the first place.