Not sure where your getting the white flash. Whatever background color you set for the movie will continue through scenes or frames.
You can communicate with other flash movies with the local connection method. This allows you to use a flash movie in one frame and manipulate a flash movie in another frame.
I wrote a tutorial about Flash and PHP integration to create a Content Management System for flash. It also describes how to create a newsreader section that allows for external updates...
Hope it helps
A mind once stretched by a new idea never regains its original dimensions.
- Oliver Wendell Holmes