Is it a picture u want to use or a pattern???
U can use CSS to set the alignment and size of the background... You can make it a single image in te center or let it repeat vertically or horizontally...
This is how it's supposed to look:
Code:
<style type="text/css">
body
{
background-image: url("/images/background.gif");
background-repeat: no-repeat;
background-position: center center
}
</style>
Read more about it
here
(BTW.. M0g. This probably belongs in the HTML/CSS section)