var WindowObjectReference = null; // global variable
                    
function openPopup(strUrl, strWidth, strHeight)
{
  strProperties = "width=" + strWidth + ",height=" + strHeight + ",location=no,menubar=no,resizable=no,scrollbars=no,toolbar=no"
  if(WindowObjectReference != null)
  {
    WindowObjectReference.close();
  }
  WindowObjectReference = window.open(strUrl, "zzzpPopup", strProperties);
  WindowObjectReference.focus();
}