А так?
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Без имени</title>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
</head>
<script type="text/javascript">
<!--
function _submit() {
window.open('','new_win','width=400,height=200,location=no,toolbar=no,menubar=no,status=no,scrollbars=yes,resizable=yes');
}
//-->
</script>
<body>
<form action= "" onsubmit="_submit()" target = "new_win" method="POST" ></form>
</body>
</html>