Full screen, fixed aspect ratio, non scrolling background?

I am trying to emulate an effect like this site uses…

and I’ve basically poached their script, a jQuery initiated 100% width and height background that loads into a couple of holding containers.

The thing I would like to do differently is fix the background in place so the content can scroll over it. How can I, say, write the flash movie to the BODY background or something like that? I’m not a javascript wiz and am not sure how I might do this.

Anyone have any ideas? Alternate solutions? Any help would be greatly appreciated.