Check out this page. http://www.linuxguruz.com/iptables/
There are some scripts and the one that multi-homed should be what you are after. Use it myself for a start with 5 nic setup. Currently only using 4. The fourth is the wireless side. 5th was for second channel internet bonding. Never got it quite right yet.
If you mean ipchains and iptables. They are two completely seperate packet filtering tools. iptables is used on newer 2.4 and current 2.6 kernels. ipchains was in maybe early 2.4 and 2.2 kernels. ipfrwd I think was in 2.0 kernels.