Reference Nested Movie Clips with ActionScript 3 in Flash CS5
http://www.access2learn.com/
This short tutorial shows how to control movie clips and nested movie clips with ActionScript. You can control the playback and other properties using the . (dot) between instance names.
Start with the outermost movieclip, and work your way in: ex:
grandparent.parent.child.gotoAndPlay(25).