Code: 
<script language="JavaScript">
window.open("popup.htm",
"NamedesFensters","width=250,height=400,scrollbars=yes,toolbar=no,directories=no,status=no,resize=yes,menubar=no");
</script>
oder per Click:
Code: 
<a href="#" onclick=window.open("popup.htm","NamedesFensters",
"height=400,width=250,scrollbars=yes,toolbar=no,directories=no,status=no,resize=yes,menubar=no")>Popup</a>