Hi Edvard,
You need to set your router (Adsl router?) to allow incoming connections.
In other words the IP address you see at myip.dk, is not the IP address of your computer. It is the IP address of your _router_. (You can prove this by going to more than 1 machine on your lan, and going to that web site. Notice they all return the _same_ ip address, the address of your _router_.)
So (typically) using your browser, go to your router setup, and set incoming connections on port 80, to be routed to the specific machine on your lan where the program is running.
Cheers
Bruce