Full screen background with content always centered


Can anyone please help with the following: Tutorial http://www.kirupa.com/developer/as3/resizing_centering_as3.htm

I have gone through it all and it works great for the tutorial but I tried replacing the background with an image and when the browser is resized to full screen it distorts the image and stretches it out of proportion. Does anyone know how I can have the background image resized to the full screen and stay in proportion?

I basically want to create the exact functionality as www.cafeinternational.ca

Any help will be much appreciated.

Thanks in advance.