How can I constain the aspect ratio of a dynamic image?

programming flash
1

This is the site I’m working on…
http://www.bus15.com/clients/shalowitz/Flash/

and here’s what I’d like to do…

You see the image being loaded into the background (which is a duplicate of the current image being displayed) is currently set to:

backgroundMC._width = Stage.width;
backgroundMC._height = Stage.height;

However, ideally, I’d like the image to fill the screen without distorting the aspect ratio of the image and center itself on the screen. Does anyone know if this is possible?

Thanks!