I came across a flash screen cast a few days ago that buffered immediately, and preserved the Vista desktop the way it should be. It's called Jing, and isn't a beta or a final product, it's a project. It works on Mac and Windows!
The interface freaking rocks, and it allows you to upload your videos or annotated screenshots anywhere via Flickr, their own hosting website or any FTP server of your choice. I know I'll most definitely be using it alongside Window Clippings if someone ever needs to have something explained to them quickly and easily - it's just so cool, and produces flash video too! This makes the output files really easy to send to people, as their browser will just start playing them.
Below is a screen cast I made with the software for testing purposes, using Firefox 3 RC2 and Notepad 2. It even supports input from a microphone too, which is absolutely amazing for a free piece of software. (Well, for now anyway. I will totally get this if it becomes a paid for product though.)