Auto-size vs. fixed movie size

I wasn’t sure where to put this post. I hope this is the right place.

This is what I want to do:

On screen resolutions up to 800x600, I want my Flash movie to resize to 100% width and height of the browser window. On screen resolutions higher than 800x600, I want the Flash movie to be a fixed size (say 800px x 600px exactly).

Is this possible, and if so, how?