Movieclip scaling

I am trying to implement a own scrollbar component, based on the simple cusom scrollbar:[COLOR=#008000][/COLOR]

My proble is that I want the conent to be dyamic, varing in size. For this I need the scollbar dragger to change in size depending on content size. What is th best way to change size for a movieclip dynamic loaded from library? Scaling seems difficult, I want to be able change the size for the movieclip to a certain height. Anybody have a method for it? My plan is to createemptyMovieclip and the attach the movieclip from library and resize it.