var popwindow = null;
          
    function pop(url, name, width, height)
    {
       if (!popwindow || popwindow.closed)
       {
          popwindow = window.open(url, name, "height=" + height + ",width=" + width + 
                      ",toolbar=yes,location=no,directories=no,status=yes,menubar=yes,scrollbars=yes,resizable=yes,left=50,top=50");
          popwindow.focus();
       }
       else
          popwindow.focus();
    }