[CentOS] IPTables help

I have a dual homed server in an install for someone who is very cost sensitive. This server originally is being setup as an Asterisk server, but now the simplest thing for me to do is also set it up to provide internet access for the small shop as well.

So it will have one external, WAN facing nic that needs all incoming ports except UDP 5060 and 10000 -> 60000 blocked for all but two ips.

The internal, LAN facing NIC will need all ports except voip/dns/http blocked to it, and need to provide masquerading.

I have limited experience with iptables and would love some guidelines. Any pointers would be greatly appreciated!

Thanks, jlc