If you are doing a presentation and wants your desktop to be captured to the video (instead of the camera pointing at the screen) download and install the following:

For Mac: http://www.varasoftware.com/downloads/DesktopPresenter.dmg
Windows: http://www.varasoftware.com/downloads/DesktopPresenter.exe

In Windows, it helps if you install Bonjour for Windows:
http://www.apple.com/support/downloads/bonjourforwindows.html