I still can't really work out what you are trying to do as that page looks odd (especially with all the scrollbars) and I can't follow your logic.:)
If you want an image behind elements then why don't you use a background image anyway?
You can get the image behind the content by raising the z-index on the content.
However I think you need to re-think what you are trying to achieve here as that page looks very messy and everything is all over the place. Get rid of the scrollbars in the middle and side columns and give the header a min-width to stop it wrapping . You can't let it wrap because you have given it a fixed height and it will overlap if it wraps.