natd & port mapping

So I set up internet sharing using natd, dhcp and the most simple, unintrusive set of firewall rules. So now I need port mapping. I wrote up a bunch of rules and stuck them in /etc/natd.conf . The only problem is, after restarting natd, it doesn't seem to have 'picked up' these rules. Is this the right place to put my rules? Or do I need to stick them someplace else?