try these links that explain you step by step : http://www.siliconvalleyccie.com/lin...dns-static.htm and
As far as the firewall try firestarter for 2 NICs or shorewall for 3 NICs.
to update use yum install <package name>: yum install firestarter
My Linux box is Fedora core 4. I am using now the firestarter which has a very friendly GUI. With firestarter, you can see the IN/ OUT traffic. I will test Shorewall because i need 3 NICs.
FC5 has some installation bugs as far as for me.