Fullscreen flash movie that dosen't distort???

Hi i have created a fullscreen flash movie with actionscript and html, the background is full screen and stretches with the browser but the background image i used skews and warps if you stretch the browser up or down. I want the image not to warp but grow along with the browser...
Here is a example at burnkit.com in the "company" section.

I think it is just a simple code i need to add. Any help greatly appreciated. Thanks:]