примерно так:
Код:
<html>
<head>
<script language="javascript" type="text/javascript">
var win=null;
function openwin(mypage,myname,w,h){
LeftPosition= (screen.width)?(screen.width-w)/2:100;
TopPosition=(screen.height)?(screen.height-h)/2:100;
settings='width='+w+',height='+h+',top='+TopPosition+',left='+LeftPosition+',scrollbars=no,
location=no,directories=no,status=yes,menubar=no,toolbar=no,resizable=no';
window.open(mypage,myname,settings);
}
</script>
</head>
<body>
<a href='' onClick="openwin('your.html','windowname',100,100)">open!</a>
</body>
</html>