var message="Beachten Sie bitte das Copyright!";

  function click(e) {
    if (document.all) {
      if (event.button==2||event.button==3) {
        alert(message);
        return false;
      }
    }
    if (document.layers) {
      if (e.which == 3) {
        alert(message);
        return false;
      }
    }
  }

  if (document.layers) {
    document.captureEvents(Event.MOUSEDOWN);
  }

  document.onmousedown=click;