Well first, Here's the code:
<style type="text/css"> body{background:url(url here)} </style><b style=position:absolute;left:137;top:15;ptsize:3pt;></i>Background by: url or credits go here</b>

Where it says url here of course you put th url there and where it says url or credits here you put the url of your site, your cren name on neopets, email address, name, or any thing you want for the crediting of the person who made that backgorund. (bg)