You should leave it as port 8000. And your current icecast and SAM config should be alright. If you're able to connect to the stream on the server itself(your computer), then it's set up correctly. Other computers in your network would connect to the stream using your static internal IP. However, outside computers need to connect through your external IP.
But anyway, could you get me a screenshot of the DMZ section of your router's config? If port forwarding hasn't work, then that's the next step.
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We've solved this problem via PM. This topic can be closed now.
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Well, I guess I should actually add on a bit in case someone else runs into a similar problem and searches for an answer.
Some of these things might be specific to icecast, but I believe it applies generally:
Making his computer DMZ did solve the problem, however I don't condone doing this just because it works. This exposes your computer completely to the internet. While a router's security certainly isn't impenetrable, it does help. If anyone else does this, you should be sure that the computer you're setting up as a DMZ has a properly configured software firewall on it(although you *should* have that on any computer).
Another note, the Windows Firewall that is provided on Windows XP SP2, Server 2003 SP1, and any version of Vista can be responsible for blocking connections to your server. It is definitely a good idea to test if this is the cause of your problem before setting the server as a DMZ. Since I have no idea about the firewall differences between different Windows versions, I'm just going to say that you should google configuring the windows firewall on whichever OS you're using.
And lastly, I need to be clear on one thing. Any computer within your network *cannot* test the server through the external IP. If you simply go to another computer in your house to test your server, you can only connect through the server's *internal* IP(which more than likely begins with 192.168). In order to test if external computers can connect to your server, you have to test with an external computer.