Mac as Network Bridge

Ok, I've got a mac laptop and I'd like to know if it's possible for me to use my machine as an ethernet bridge.

The idea is to connect an xbox to the internet/network through the ethernet card and AirPort of my machine. The AirPort is connected to a wireless-g router which in turn normally gives my laptop access to the router's little private network and the internet.

Can what I am asking be done with the System Preferences or a 3rd party app?

I think that it should be theoretically possible, but the nuances of mac network configuration still escape me after owning one for a whole month. Thanks for the feedback in advance. 😀

That rocks, thanks a ton!

Alright, so that sounds pretty simple. In fact, I partly tried to do that already, but I wasn't quite sure what the "Share" option would do. None of the language really conveyed what, at the data level, would be going on... But if it works, which I'm sure will be the case when I open those ports, it'll definitely be another great thing that I find out about MacOS X.
Thanks a lot for your time!

Actually...

Actually, that didn't really work at all... even with a crossover cable... the Xbox didn't get an IP address from my computer, and there wasn't a way for me to get it one...

Also, my ethernet connection remained in the "no ip-address" mode with a yellow light next to it. Makes me think that the computer didn't even know that it was supposed to be the DHCP server for that connection.

I don't know how it should have worked, but we've got it on a WinXP laptop right now, and that's working fine. Thanks for the list of ports too, btw. If anyone's got any thoughts about the Mac internet sharing, that would be nice to hear about.