Background image won’t center!

Ok, this is my background image:

http://www.dizzytech.com/realm/wp-content/themes/default_allsidebar/images/bgm.jpg

This is the code used in my stylesheet:

body { background: url("<?php bloginfo('stylesheet_directory'); ?>/images/bgm.jpg") repeat-y; background-position: center center ; background-color: #fff;
}

Even though I have the “background-position: center center ;” part, it still looks like this:

http://www.dizzytech.com/realm/index2.php

Help?!