Unfortunately, it isn't good to reply to your own message on this system, because it looks like you've received an answer. Many here will search for zero reply threads, even if they're a few days old.
I'm not familiar with this Darwin Streaming server. However I do know there are netblocks reserved for video and audio streaming, which I'm a little vague on. However I did see on the video blog Mediabytes that one ISP is blocking video streaming.
From an external IP address, try using nc (NetCat) to open ports on your streaming server. On your server, use tcpdump to confirm your streaming on the ports you think you are. And use nmap on your external public ip address to see which ports are open, closed or blocked.