[Dagoor]

well its just the matter of replacing your header files with the images you want...
you header is consist of two things (right click to know the exact location of the images so you can replace them:

one is the left image:


and the repeated background that goes beneath it:


look how if you put this two images together its continuous.

(without the white gaps)

so create something in photoshop that you can extend its right side and just like the one above have your extended right side as the background.