background images cannot be stretched unelss you use CSS3. CSS3 hasn't been ratified yet, so you may or may not get the desired result across all browsers (especially older browser versions)
then you'd have to master the "onresize" event of the window object to query all the elements on your page and then, using some algorithm, resize the elements.
pretty tall order.
if you want to give it a try, i'm sure many of us could debug your code along the way. be sure to offer an example page for debugging!