Sorry you're having trouble with this feature. Do you have the new Windows Live Movie Maker, or the original Windows Movie Maker? It will say either "Windows Live Movie Maker" or "Windows Movie Maker" at the top of the window.
Songsmith only knows how to open up Windows Movie Maker (the older program) automatically. However, this feature is really just a convenience: both Windows Movie Maker and Windows Live Move Maker can import audio files (i.e. add a soundtrack to your
movie), so you can always just save your Songsmith creations as an audio file and bring that audio file into either version of Movie Maker.
Hope that helps... good luck!
-Dan from the Songsmith Team