Full-width header, narrower content area?

I can't figure out how to accomplish a layout like this: http://wcbstv.com/ with Atahualpa.

I tried setting the layout to 100% to get the header to span the full width of the browser window. OK, that worked. Then I thought I could set the left and right sidebars to be 100px wide, and the inner left and right sidebars to be 200px wide. I'd leave the right and left sidebars empty, essentially creating blank space, so the inner 2 sidebars would contain the widgets and the center column would contain the content.

I think this could work, but what happens is that the page and category menus span the full width, along with the header image. I want them to stay just spanning the 2 inner sidebars and center column. Could that be done with CSS margin values?

Can you think of some other way to produce this effect?