[shan]

or something like this

{literal}
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_openBrWindow(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}
//-->
</script>
{/literal}
<a onClick="MM_openBrWindow('popup_window.php','popupname','width=400,height=275')" >Click Here</a>