How can I tell a external .swf to start playing?

Hi everybody!

I need help with telling a external movie(.swf file) to start play when I click
on a button.

I have made a site in dreamweaver where the topframe is in flash and the
middleframe in html and the bottomframe in flash.
I have 2 buttons on the topframe and I want when I click on one of them the
bottom flash file starts to play.

How do I do this??