you are using an image tag for the background, instead, the image should be added as a background to the body using css.
see this page or details on creating a full page background using CSS:
http://css-tricks.com/perfect-full-page-background-image/
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.