var RollOver = Class.create();
RollOver.prototype = {
initialize: function(option) {
  var props = { //?????????
    hclass : "hover", //class=rollover??????
    suffix : "_o" //?????????????_ovr???????
  };
  if(option) for(var key in option) props[key] = option[key];
  $$('img.'+props.hclass,'input.'+props.hclass).each(
    function(el){
      var osrc = el.getAttribute('src');
      if (!osrc) return;
      var hsrc = osrc.replace(/(\.gif|\.jpg)/,props.suffix+'$1');
      (new Image()).src = hsrc; //?????????
      el.observe("mouseover",function(){
        el.setAttribute('src', hsrc);
      }).observe("mouseout",function(){
        el.setAttribute('src', osrc);
      });
    }
  );
}
}//prototype
Event.observe(window,'load',function(){new RollOver();});