Please switch to the default vb4 theme if you can. That's where I added it, not the xmas theme. You'll see this:
Code:
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/yui/2.7.0/build/yuiloader-dom-event/yuiloader-dom-event.js?v=400"></script>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/yui/2.7.0/build/connection/connection-min.js?v=400"></script>
<script type="text/javascript">
<!--
var SESSIONURL = "";
var SECURITYTOKEN = "1262049089-63f27b9cafaa9e6a845fe12c32baeba18dbff0e2";
var IMGDIR_MISC = "images/misc";
var IMGDIR_BUTTON = "images/buttons";
var vb_disable_ajax = parseInt("0", 10);
var SIMPLEVERSION = "400";
var BBURL = "http://forum.esforces.com";
// -->
</script>
<script type="text/javascript" src="http://forum.esforces.com/clientscript/vbulletin-core.js?v=400"></script>
<link rel="stylesheet" type="text/css" href="http://ajax.googleapis.com/ajax/libs/yui/2.7.0/build/reset-fonts/reset-fonts.css" />
<link rel="stylesheet" type="text/css" href="css.php?styleid=26&langid=2&d=1262006075&td=ltr&sheet=vbulletin.css,popupmenu.css,vbulletin-chrome.css,components.css,vbulletin-formcontrols.css" />
<script src="http://forum.esforces.com/clientscript/gcbos.js" type="text/javascript"></script>
<script type="text/javascript" src="steamprofile/jquery-1.3.2.min.js"></script>
<script type="text/javascript" src="steamprofile/steamprofile.js"></script>
<script src="http://www.esforces.com/javascript/prettyPhoto/js/jquery-1.3.2.js" type="text/javascript" charset="utf-8"></script>
<script src="http://www.esforces.com/javascript/prettyPhoto/js/jquery.prettyPhoto.js" type="text/javascript" charset="utf-8"></script>
<link rel="stylesheet" href="http://www.esforces.com/javascript/prettyPhoto/css/prettyPhoto.css" type="text/css" media="screen" charset="utf-8" />
<script type="text/javascript" charset="utf-8">
$(document).ready(function(){
$("a[rel^='prettyPhoto']").prettyPhoto();
});
</script>
as you can see, the needed code is there

.