Yes, it wouldn't be too difficult. I assume you mean that the text to be written in glass? Or literally the video playing within the bounds of the text? Both are fairly straight forward to do, but if you've never used Motion before (or used it a little) you will probably find this extremely difficult. To say that Motion has a steep learning curve would be an understatement!!
It has so many little annoyances, like when you open it you have to open the layers tab (cmd+5) just to get started... Should really be there by default. Haven't seen Motion 4 in action just yet though. Midway through something so pointless to upgrade yet.
