var loaded = false;

  function startLoading() {
    loaded = false;
    showLoadingImage();
  }

  function showLoadingImage() {
    var el = document.getElementById("load_wait");
    if (el && !loaded) {
        el.innerHTML = '<img src="js/loader.gif" alt="" />';
        new Element.show('load_wait');
    }
  }
   function stopLoading() {
    Element.hide('load_wait');
    loaded = true;
  }

   Ajax.Responders.register({
    onCreate : startLoading,
    onComplete : stopLoading
  });