The thing that was done with haredo was to eliminate the logo and sales text and basically empty the logoWrapper.
Right now, a basic Zen main page has
If you turned it into
by removing the entire logoWrapper div and its contents from the templates/YOUR_TEMPLATE/common/tpl_header.php file, you can then concentrate on using a background image in the headerWrapper to replace the other logos. The wrapper will need to be set to whatever height you make your banner. You will need to make the banner the same width as the site. Trying to do a 100% banner can be done but it is VERY tricky. Best to decide on something like 925px and make both the site and the header that width. Haredo used 750.
Note that the upper left and right corners have nothing but color in them so that the "Home | Login" and Search float right on top of the image.
Your stylesheet would reflect something like
You could combine your current log.gif (251 x 236) with the head2.jpg (549 x 236) into one headerwrapper.gif it would already be 800px wide. You could adjust accordingly to make it the width you need. It's what you did on the main site for your header.