Mixi.Common.Namespace.createNamespace('Mixi.Media.ImageRollOver',function(){
    $$('img[src*="_off."]').each(function(img){
        // preloading
        var _dum = new Image();
        _dum.src = img.src.replace(/_off\./, "_on.");

        // event handle
        img.observe('mouseover',function(evt){
            this.src = this.src.replace(/_off\./, "_on.");
        });
        img.observe('mouseout',function(evt){
            this.src = this.src.replace(/_on\./, "_off.");
        });
    });
});