Port Forwarding And Internet Sharing


I've been using my mac just as a general workstation for a bit - running Mac OS X 10.2.8 - its connected to my Cable Internet connection via an airport.

I recently decided it would be a good idea to move a few other computers into the same room as the mac. Because the Mac is the only one with the wireless card, I thought I'd give Internet sharing a try - turned it on, plugged the Mac into my hub and voila all my other machines can connect to the net through it.

Now - I'm trying to do a port forward on the mac to port forward calls to say Port 80 or Port 22 to another computer in my network - and I just can't figure out where to do it. If it was Linux I'd use the IPTABLES - but I don't see a setup like that. There is NATd but not super familiar with how it works. I downloaded a little app called gNAT but that only sets up what I already have -

Is there a way to port forward requests to through the Mac to another local machine?

thanks in advance