eddydreni is right about not needing a software firewall if you're behind a router. Obviously this means your outgoing connections are unfiltered unless you set up filtering of outgoing connections on your router. Personally, on PCs which I use and control, I don't use software firewalls if I'm behind a NAT router. This is because I'm very careful with the software I install, and the websites I browse and I always keep my PCs patched and up to date. I still however advise the use of software firewalls such as ZoneAlarm or Kerio even when behind routers, if you are unsure of the user's habits or security consciousness. Of course if you have control of the router you can control outgoing connections. So digen's suggestion is also correct. As with most things computing, it's going to be "horses for courses"
