[CentOS] How to setup a computer using CentOS6 as a firewall for the whole network in my place?

Hello
in one of the emails I sent earlier ; mark (m.roth at 5-cent.us) mentioned:

>     install linux on a computer with two ethernet cards.  connect eth0 to
>     your internet connection, and eth1 to your local network.   configure
>     iptables firewall rules in the linux system.  or install pfsense on that
>     same computer.

Please if any one can help with more details and example for the 
configuration that would be awesome.

Thanks