I have done this a few times.
Basically you have to do math calculations in JavaScript based on the browser's window size. I think the syntax is something like screen.width, screen.height. Or maybe that is for the screen size. Anyway, the syntax for the browser window is similar.
Then use JavaScript/DHTML to tell the layer(s) exactly where you wante them situated. Using CSS you have to tell the layers that they are "position:absolute" and then set the "top" and "left" using your DHTML.
Sorry I don't have any code for you, lemme know if this is good enough.