An important bit of information that you require is the last frame number in your movie. Now, in your Preloader scene, place two keyframes, one in frame one and the other in frame two. Select the first keyframe add the following actions:
If Frame Is Loaded (MovieScene, 350)
// if the last frame of the movie is loaded
Go to and Play (MovieScene, 1)
// go to and play the movie
End Frame Loaded