Most routers made in 2005 or newer have integrated NAT, which is at least some form of protection. Despite this fact, having a software based firewall is still a good idea. I run everything through routers and port switches. The chances of a security breach are slim, but I still use Windows Firewall. I haven't had to use anything else, but then again I've been behind a router since the first day I upgraded from dialup so that might be why.........
EDIT:
I shouldn't be saying this seeing as I have a public server, but hardware based network security has never been my forte.
