PowerPoint does have a QuickTime export option, it's under Save As... and then pick "Movie" as the format. I believe if you use the Record Narration function in PowerPoint, it will export in the movie. (I have not tried this though)
What I usually do though, is to import my PowerPoint files into Keynote, make sure the formatting is all OK, and export to QuickTime from Keynote. It usually looks a lot better, and you have more QuickTime options.