Probá a ver si te sirve el siguiente código:
<pre>
<html>
<head>
<title> New Document </title>
<script language="javascript">
var win = null;
function nuevaVentana(pagina,nombre,w,h,scroll){
LeftPosition = (screen.width) ? (screen.width-w)/2 : 0;
TopPosition = (screen.height) ? (screen.height-h)/2 : 0;
estilo =
'height='+h+',width='+w+',top='+TopPosition+',left ='+LeftPosition+',scrollbars='+scroll+',resizable'
win = window.open(pagina,nombre,estilo)
}
</script>
</head>
<body onLoad="nuevaVentana(this.href,'name','300',' 200','yes');return false">
</body>
</html> </pre>
<hr noshade size=1 color="#000000"><img src="http://www.gograph.com/Images-8712/ClipArt/cat03.gif" height="50" border=0 align="absmiddle"> <font size="2" face="verdana" color="#000000">
bet[/CODE]