function change_img(obj, active_prefix, over_prefix) {
       obj.run = obj.run == null ? 1 : 0;
       if(obj.run) {
              active_prefix = active_prefix || '_active';
              over_prefix = over_prefix || '_over';
              obj.active_link = (new Image()).src = obj.src.substr(0, obj.src.lastIndexOf('.')) + active_prefix + obj.src.substr(obj.src.lastIndexOf('.'));
              obj.over_link = (new Image()).src = obj.src.substr(0, obj.src.lastIndexOf('.')) + over_prefix + obj.src.substr(obj.src.lastIndexOf('.'));
       
              if(location.href.match(new RegExp(obj.parentNode.href + "$"))) obj.src = obj.active_link;
              else {
                     obj.old_src = obj.src;
                     obj.onmouseover = function() { this.src = this.over_link }
                     obj.onmouseout = function() { this.src = this.old_src }
                     }
       }
}