Believe it or not, the Microsoft Windows Media Encoder can take a video screen capture of the region of your screen where the video is playing, and it will record the video and sound, and also compress and save the file, all at the same time.
Download Page
If you still want to record the web cast, you can.
I'll post step by step instructions as soon as I write them...
By the way, I don't think the recorder mentioned above will do just a region of the screen.
UPDATE BELOW