Do I need a hardware firewall?

I have recently upgraded to broadband service and I'm a little more concerned about security now that I have an always-on connection.  Our current network consists of three computers, linked together through phoneline network cards, with one computer serving as the host for internet connection sharing.  All three computers have Sygate Personal Firewall software installed.  However, after running some online port scans, I am concerned that the software firewall is inadequate.  Will a hardware router with a built-in firewall give me additional protection?

 

Thanks!