A scrolling background should be somewhat bland. You don't want people to realize that it is the same movie playing over and over.
The easiest way to create a scrolling background is to have to copies of the movie next to each other. The first one moves across the stage until it leaves on the left, then restarts. The second one is off the stage to star and is always right behind the first one.
INDEX, Animation in Flash, Frame Animation: A traffic light, Demonstration: Creating the traffic light, Motion Tween: A swimming fish, Shape Tweening: From a red square to a blue circle, Shape Tweening Demonstration: From a red square to a blue circle, Property Tweening: Changing the alpha value, Property Tweening Demo: Changing the alpha value, A Scrolling Background, Create a Scrolling Background Demo
Next lesson: The Bone Tool
