Has anyone any experience with "Guard Dog" Firewall

I'm just learning the LINUX OS and I was wondering if anyone has used
the firewall "Guard Dog" on a workstation that is hooked to the internet
through an Ethernet router? I just want to learn a little about
firewalls. I also have the Mandrake Client firewall software, but I'm
not sure if it's beyond my understanding just now.
John Steele