How do I make a scrolling background that does not repeat infinately?

Im using Adobe Actionscript 3.0 with Air 2.5, and I was just wondering how to make a background scroll while making a sprite move up and down with user control and during a timeline. Any help will be appreciated as I am having great amounts of trouble of how to start this project. I will include the source of the code once Im done with the app. Thanks!