However, if you export the file into movie format so that it could be played on computers with no Powerpoint, the narration is lost.
Just discovered this while trying to do just that. As a result, am now conducting google searches to see if there is a work-around. But the first thing I found was this item in Microsoft Office that says exactly what I didn't want to read: Narration is not saved when you save a presentation as a movie.
UPDATE: Could not find any solutions on the internet. Fortunately, the project I was working on was fairly short and simple. I wound up doing everything in Keynote and that exports to movie with no problem.