Or for a much better solution, grab an old Pentium PC (you know the free ones that sit on the curbs waiting for the garbagemen) and build a nice Linux based gateway. If you are nervous about IPChains etc... then use one of the "turn-key" packages available.
One of the best is Clark Connect. Besides - it's free and it's Canadian!
ClarkConnect
I've got a very large network in my house (Mac's, Sun's, HP's, PC's, printers etc...) and it works great. It works as an FTP server, Apache Web server, Samba (Windows) server, Netatalk (AppleTalk) server, SSH server and much more!
I didn't mean to make this sound like an infomercial, but everytime I use one of those router-in-a-box solutions at other people's places I really miss the configurability of my Linux boxes... I just got back from the west coast and it seems that most places I stay at want me to swap computer admin/home theater guru services for room and board.
So if you're a techno geek with some Linux/Unix interest (and you should - it will help with OS X), try it out.