Alright, if you have the ustream account and ustream producer I can help.
-If you are doing a webcam or video capture, etc. choose the "live input" icon.
-You get to pick a video source, and a method of sound from a quick pop-up tab. After you make the two selections, click on the "add live input" at the top of that tab. Just click on the "live input" icon to bring that tab up again.
Once you do that, a small screen at the bottom will appear below with whatever the device is recording. If you click on it, that image should pop-up in the center of the ustream producer showing you what you are watching. You can adjust audio levels on the right side of the window. In the bottom right, there is a thing for broadcast. If you pick that, you will start broadcasting. Click again to stop.
Now, if you are trying to do a screen capture (stuff from your screen), simply select the "screencast" by double clicking. You'll be given a small pop-up window. You can make selections from it. You select the "source" which is either you screen itself, or a window you have up. If you choose, window, you'll be asked for an "application" that you currently have running. After that, you can choose a different "window" if you have multiple of the same application running (ie. you have firefox windows running). Somethings require you to select that 3D compatibility in order for it to show properly. So, I would select it everytime you do a screencast just encase.
I still have not been able to figure out how to get in-game audio from the visual boy advance apart from running a microphone. The video capture device I have lets me have the in-game audio.