function addEvent(type, fn, target){
  target = target || window;
  if(target.addEventListener){
    target.addEventListener(type, fn, false);
  }else if(target.attachEvent){
    target.attachEvent("on"+type, fn);
  }
}

addEvent("load", function(){
  var imgs = document.getElementsByTagName("img");
  var hover_init = function(img){
    addEvent("mouseover", function(){
      img.src = img.src.replace(".png", "_h.png");
    }, img);
    var mouseout = function(){
      img.src = img.src.replace("_h.png", ".png");
    };
    addEvent("mouseout", mouseout, img);
    addEvent("click", mouseout, img);
  };
  for(var i=0; i<imgs.length; i++){
    var img = imgs[i];
    if(img.className.match(/hover/)){
      hover_init(img);
    }
  }
});