var switchImg = function(st){
  var is_on = st;
  return function(e){
    var elm = Event.element(e);
    if (!is_on){
      m = elm.src.match(/(1|off)\./);
      if (m) elm.src = elm.src.replace(/(1|off)\./, (m[1] == 1 ? '2' : 'on')+'.');
    }else{
      m = elm.src.match(/(2|on)\./);
      if (m) elm.src = elm.src.replace(/(2|on)\./, (m[1] == 2 ? '1' : 'off')+'.');
    }
  };
};
Event.observe(window, 'load',
              function(e){
                var imgs = document.getElementsByClassName('switchImg');
                if(imgs == false){
                  imgs = Element.getElementsByClassName(document, 'switchImg');
                }
                if (imgs){
                  for (var i = 0; i< imgs.length; i++){
                    if ((m = imgs[i].src.match(/(1|off)\./))){
                      (new Image()).src = imgs[i].src.replace(/(1|off)\./, (m[1] == 1 ? '2' : 'on')+'.' );
                      Event.observe(imgs[i], 'mouseover', switchImg(false));
                      Event.observe(imgs[i], 'mouseout', switchImg(true));
                    }
                  }
                }});