How do I connect a VGA input to my Mac? I am not talking about connecting a VGA monitor to a Mac. I'm referring to plugging in a VGA output in to my Mac. I want the VGA to show up as a video device, so that I can run a projector's feed through UStream. 

What hardware is needed to digitize a VGA input in real time to send for broadcast?
I use a product from http://xlr8.com/ to give me a video input on my mac, then use a VGA-to-TV adapter to stream powerpoint over ustream.  Video is really choppy and crappy looking, but for simple non-moving slides, it's OK for ustream.