Develop Windows code to continuously capture screen shots, encode as [url removed, login to view] (MPEG), send in Flash RTMP protocol to Wowza for distribution as live video stream.
You can download a product that already does this to see how it works.
See [url removed, login to view], procaster. It is free to download and use.
My users want to stream video of themselves while playing fullscreen DirectX games such as World of Warcraft. I'm not sure this makes a difference in the way the screen is captured. I don't think it does. I've read somewhere the procaster captures the screen via DirectX.