I'm not sure if I understood the question, and I won't go into it too much here since this IS a php forums, but...
At the appropriate frame in the timeline of your movie, have your smaller MC load on a layer above your main movie. Then, all you need to do is include a button in the smaller mc that will point the main movie to load a certain frame. Right now I don't have Flash open, but I'd look at your movie control functions. Seems to me you can set an action event like "on press _root goto and play 20".
I'm by no means a flash expert, but I know I've done what you want to accomplish and it was somewhere down that road.