Hey,
No one replied so I figure it's worth a shot.. Maybe I can help a bit.
Do you use a router?
Your problem sounds like Port issues, you should look into forwarding the required ports for Two Worlds on your router.
If you havn't been through this before with anything else, you may need to make a Static IP
There are step by step instructions for a vast range of routers (and information on setting up a static IP) on this site.
http://portforward.com/
They also have a vast list of games and applications and their required ports. A few clicks in and it will have a webpage with instructions specific to your router and the game/app selected. (I check, it has Two Worlds in the list.)
Hope this helps you, and anyone else. It's all very simple but I know for myself, I had to read the static IP information a few times over slowly. :P
Goodluck!
(Edit: If your friends are playing on the same network, it could be a issue with the router they are using.)