codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento senza titolo</title>
<style type="text/css">
<!--
#container {
	height: 400px;
	width: 400px;
	margin-top: -200px;
	margin-left: -200px;
	position:absolute;
	left: 50%;
	top: 50%;
}
-->
</style>
</head>

<body>

<div id="container">
   <div id="header"></div>
   <div id="menu"><div>
   <div id="content"></div>
   <div id="clear"></div>       
   <div id="footer"></div>
</div>

</body>
</html>