var newWindow = null
   function popup(mylink, windowname, w, h)
   {
      if (!newWindow || newWindow.closed) {
         newWindow=window.open(mylink, windowname, 'toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=yes, resizable=yes, width='+w+', height='+h);
      } else {
         newWindow.focus();
      }
   }