new streaming developments - Microsoft, Akamai, Adaptive Streaming, OpenVideoPlayer etc

http://www.akamai.com/smoothhd
http://www.openvideoplayer.com/
http://stackoverflow.com/questions/397411/whats-the-best-solution-to-create-a-streaming-video-website

IIS will do Adaptive Streaming - depending on bandwidth, the quality will vary for users.

A similar architecture, but used to distribute mainly sound is the Conversations Network. They leverage Amazon S3 and EC2. The whole architecture is documented. Have a look at the interview of Doug Kaye. This project is also documented on Amazon's case studies. You dont have to use Amazon, but the concepts outlined in those articles can be reused in other projects.