Código:
<html>
<head>
<script type="text/javascript">
function pop_up(){
window.open( 'popup.html', 'Pop', 'top=50,left=80,scrollbars=0,statusbar=0,menubar=0,resizable=0,width=800,height=200' );
}
</script>
</head>
<body onLoad="javascript:pop_up();">
</body>
</html>