Messenger has two ways to share video. A video call (Actions > Video Call) is live picture and sound in both directions. The webcam (Messenger > My Webcam) sends pictures from your camera, without sound, to the friends you let watch.
Choose View Webcam on a friend. They're asked whether you may watch, and the pictures start once they agree.
In the original service, Super Webcam connected two computers directly when a webcam had a single viewer, to send larger pictures more often than Yahoo's servers allowed. Here every picture goes through our server, at the highest rate and size Messenger supports, for every viewer. That is why the webcam window says Super Webcam mode is unavailable: you aren't missing anything, and nobody learns your computer's address.