Originally Posted by djfusion
Are your computer and 360 hooked up to a router? If so, I think it's a safe bet that the port isn't actually in use, but is being blocked by your router. This means that you'll need to tell the router to allow the set of ports you need (depending on the router this is called "Port Forwarding") to the IP of the Xbox, and if you wanna be safe, your Mac as well.
Yeah, I tried that too. No dice.