Okay, I just tried it, and here’s what I did.
Dimensions: Percent (100 x 100)
HTML Alignment: Default
Scale: Exact Fit
Flash Alignment - Horizontal: Left Vertical: Top
That will force the flash movie to stretch to fit the majority of any browser screen. There will be a gap around the movie because flash doesn’t add the required code into the HTML body tag.
If you want to have no gap, then add this to the body tag in the HTML file
marginwidth=0 marginheight=0 leftmargin=0 rightmargin=0 topmargin=0 bottommargin=0