Just to clarify one thing... you can have other people access your server WITHOUT donating... you need to donate to be able to use the PREMIUM features, which include streaming using any application BESIDES the built in web interface for streaming.
That being said, I imagine that your computer is behind a firewall that you do not have control over. Quick test:
If you go to a command prompt and type "IPCONFIG" (assuming windows is the operating system) you will see a line that says "IP Address."
Now go to this web site:
http://www.whatismyip.org
Does the IP address shown match the IP address displayed in the IPCONFIG command?
If not, there is something between you and the outside world providing Network Address Translation (NAT) services for you, and if you do not have access to that device, you will probably be out of luck.
HTH. Let us know how you get on (but I do NOT recommend you post the details of the above test to the forums).
Glenn