popupWindow = null;

function popup(src, w, h)
{


  if(window.screen)
  {
   aw=screen.availWidth;
   ah=screen.availHeight;
  }
  else
  {
   aw=800;
   ah=600;
  }


  if ( popupWindow != null )
  {
    popupWindow.close();
  }

  if ( popupWindow == null || popupWindow.closed )
  {

    settings =
    "left=" + (aw-w)/2 + ","
    +"top=" + (ah-h)/2 + ","
    +"screenX=" + (aw-w)/2 + ","
    +"screenY=" + (ah-h)/2 + ","
    +"width=" + w + ","
    +"height=" + h + ","
    +"innerWidth=" + w + ","
    +"innerHeight=" + h + ","
    +"toolbar=no,"
    +"location=no,"
    +"directories=no,"
    +"status=no,"
    +"menubar=no,"
    +"scrollbars=no,"
    +"resizable=no";
    
    popupWindow = window.open(src,'popup_zoom',settings);
    
  }

  popupWindow.focus();

}