Copy this code into your "Add a Gadget: HTML" box:
<style type="text/css">
body {background-image: url("http://i205.photobucket.com/albums/bb38/idispatch4911/blog/hoppyeaster.jpg?t=1269813165"); background-position: center;
background-repeat: no-repeat; background-attachment: fixed; }
</style>
