Centrer vindue

Jeg har problemer med at få centreret et pop up vindue i denne kode. Håber på lidt hjælp hertil.

<html>
<head>
<meta http-equiv="Content-Language" content="da">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">

<script language="JavaScript" type="text/javascript" src="guide/js/callguide.js"></script>

<title>Centrer vindue</title>
<link rel="stylesheet" type="text/css" href="guide/css/style.css">
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_openBrWindow(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}
//-->
</script>
</head>

<body text="#394853" link="#394853" vlink="#394853" alink="#9FB1BC" leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">
<table width="100%" border="0" cellspacing="0" cellpadding="5">
                      <tr>
                        <td align="center" valign="middle">
                          <div align="center"><font size="2" face="Verdana, Arial, Helvetica, sans-serif"><a href="java script:void 0;" onClick="MM_openBrWindow('guide/intro/default.htm','Intro','width=975,height=699','screenX=50,screenY=50,left=50,top=50')"><br>
                            Åben centreret vindue<br>
                            </a></font></div></td>
                      </tr>
                    </table>
</body>
</html>