I’m interested in moving my background image to the front of all of my other page elements (header, sidebar, main content, etc.) to be able to overlap certain elements. Note that my background image has transparent openings that will allow me to access the other elements on the page. My goal is to basically blanket the entire site with a background image with still being able to access content through the transparent openings of my background image.
The only challenge I see is to get you to stop thinking this is a background image. It's not. You are describing a graphic layout, so use Photoshop or Fireworks to graphically design your site, then work out how to lay it out with css.
If you place a transparent.png on top of a web page you can see the page beneath it but you can't interact with it. Navigation links, for example, would be rendered useless.
Have a look at the following 3-part tutorial.
Taking a Fireworks (or Photoshop) comp to a CSS based layout in DW
Part 3 --