Found this a while ago when Scott was looking for something to do fancy things with webcam output.WebcamStudio
is basically a way to composite things like: Webcam input (from more than one webcam if needed), video playback, desktop streaming, images, irc, text, etc.. then arrange them and stream them out. As I've only just got my webcam working I've not tested the streaming output but you can check the guy who make it's uStream page
for various examples.
Though it didn't come out too well. In this picture I've got: me in the top left, the Bruce Lee ping-pong video playing bottom right (Note the slight opacity.) and my desktop playing in the background.
Going to make a uStream channel sometime this week to test out the streaming output.