Background Ad/Skin takeovers

I am looking for someone to create a background skin takeover advertising slot for my website. What I want is for the first ad to be set up with instructions as to how to change it in the future----which files to edit for the change. Also, the background ad must be clickable and be able to be assigned to specific categories or pages. Example of such background ads or skin/takeovers can be found here; [login to view URL]