I have no experience with Flash and Webcams together. the only solution I would offer, based on the idea you suggested, is to use a resized pop-up window, positioned on screen in relation to your flash movie. So in effect, you 'could' leave a gap in your movie where the pop-up would load on top, such that the rest of your movie would still be visible, though as soon as they clicked on your movie again the pop-up would disappear behind the flash html, unless there is a way using Javascript where the movie can be kept on top (I don't know).
dave davdesign@pinkzeppelin.com
^^^^^^^^^^^^^^^^^^^^^