- Linux.com's Firewall Primer: A good place to start
- Fire Wall Builder: This program will build firewalls for you. They also have a good cookbook to help you figure out what you need.
- Guarddog: "Protecting your computer with a cute little dog," is what they say, but it's a fairly decent GUI firewall builder for Linux, IMHO.
- My 4-Line Firewall: A smart tutorial on NAT/Masquerading/forwarding
I went into my /etc/sysconfig/iptables and looked around there for some help as well. I was able to do some crude cutting and pasting, but I don't exactly know how to build a system from scratch yet.