I wanted to do the very same thing - have a video running with the
words on the bottom ... here's how to do it:
1. Insert the video clip, size it to almost full screen
2. Go to custom animation for the video clip, click on the drop down
menu for the video and select "edit timing" ... change the "stop
playing" to a high number (I typically set it at 99).
3. While I'm in the edit timing I also select "movie settings" and up
the volume of the movie.
4. View the Master Slide and make a text box along the bottom of the
slide.
5. Add the words to the bottom of the slide.
You can now play the video on the majority of the slide, with the
words on the bottom. I'm sure you can set up timing for the words to
scroll, but I just use a remote mouse to change the slides manually.
Hope that helps
Rob