Hey Tuqqer,
I have found half of the answer to our question. On the page
http://discussions.info.apple.com/WebX?14@142.W4draZqZbt8.13@.599e8fbc/0
They will tell you how to know your IP.
(by going on the website http://www.whatismyip.com/ )
However, there is still a problem: This IP is actually the one of your router, not of your computer. So how to configure the router so that it fowards any incomming traffic on the port 2000 to the computer?
I don't have an answer to that yet, but as soon as i have it, I will post it here.
It would be great: I would finally find some use to the Apache server that comes with OSX.
If I ever find out, of course...

Best regards, Daniel.