Fedora Security :: 2 Nics Internet Connection Sharing ?

I have several Proxy severs set up at our business. I always do the same basic config, except for my version of Fedora (I always grab the newest).

I put 2 nics in a machine Load Squid, Dansguardian and Firestarter. I use Firestarter to direct the surfing traffic from my LAN out a cable modem that I have for each store. This lessons the bandwidth on the T1.

Easy enough. My problem is Firestarter has always been a little flaky. But as of F11 the gui wont stay up for more than a few minutes at a time. It still functions, but you have to be quick if your going to use it because it will inevitable crash.

So I suppose it's time to start doing this the correct way and using IP Tables. Does anybody have a resource they can point me to that will help me understand how to do this? It looks like this might be as simple as setting it up with the GUI Firewall tool that comes with F12 but I'm still not exactly sure how.