It is possible to play one movie and one sound simultaneously. If you want two audio tracks playing on top of each other you could embed one in a .mov and play the other as a sound, or try embedding both into the same .mov container. Not sure how to effectively do the second option without outdated software, but it could be done with something like MoviePlayer (Mac OS 9).
The first option could be executed with code like the following:
MOVIE 0 0 movie1.mov
SOUND musicsoundclip
EDIT: You could also use Quicktime Pro instead of the old MoviePlayer if you are willing to pay for a key to unlock QT's Pro features.