Hi Alexander and welcome to the community!
PPT2010 introduced some really great features including new video options. Some of those features - including text over video - aren't currently supported in Presenter '09. That's due in part because video is inserted via Presenter's Insert Video option and not PowerPoint.
One option for layering text over videos is to set it up in PPT2010 and save everything as a new video. You can then insert the video into PowerPoint via Articulate > Insert Flash Movie.
Now, if you're working with Quizmaker, you can easily layer text over video. Here's a screencast on the process: http://screenr.com/Akd