well first off, you need an account with the website. then youneed a program to capture your screen and broadcast it. Super webcam is free, but needsa few addons to broadcast live, and I havent figured teh blasted thing out yet.
I use Superwebcam, well for the 30 day trial, anyway.
then you open your screen cap program, login to ustream, set up your channel, and click "broadcast now" it brings up a popup window, when it asks for permission, grant it, Ummm
then you click on the green button that says "Broadcast" and it makes your channel go live.
then you can go ape**** :D

Yay! Thank you! X3

ManyCam 2.3 is free as well. It captures your screen and works pretty well for ustream.

I have never heard of this o.o

never heard of it >.< -shot-

Well you also need Either SuperWebcam or WebcamMax to start broadcasting.