Penso possa servire a qualcuno:

codice:
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Banner</title>
<script language="javascript" type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript">
$(function(){
	$(window).scroll(function() {
		$('#ads').stop().animate({marginTop:$(window).scrollTop()});
	});
});
</script>
<style type="text/css">
#sito{
	width:920px;/*larghezza del sito*/
	margin:auto;
	height:2000px;
	background:#ccc;
}
#ads{
	/*dimensioni del banner*/
	width:120px;
	height:400px;
	/*dimensioni del banner*/
	margin-left:460px;/* Metà della larghezza totale del sito */
	top:25px;/* Margine superiore del banner */
	overflow:hidden;/* Serve per la chiusura */
	
	position:absolute;
	left:50%;
	background:red;
	text-align:right;
}
</style>
</head>

<body>

<div id="sito"></div>


<div id="ads">
	X
	
	 
	
</div>
</body>
</html>