document.observe("dom:loaded", function(load_event) {
  new Suckerfish($$("#main_navigation ul").first());
});

var Suckerfish = Class.create({
  initialize: function(element) {
    $(element).immediateDescendants().each(function(li) {
      li.observe("mouseover", function() { li.addClassName("open") });
      li.observe("mouseout", function() { li.removeClassName("open") });      
    });
  }
});