var eventrules = {
  'div#splash_nav img' : function(element) {
    element.onmouseover = function() {
      this.src.match(/([^_]+)\.jpg/);
      this.src='/img/splash_ov_'+RegExp.$1+'.jpg';
    }
    element.onmouseout = function() {
      this.src.match(/([^_]+)\.jpg/);
      this.src='/img/splash_'+RegExp.$1+'.jpg';
    }
  }

}

Behaviour.register(eventrules);