document.observe("dom:loaded", function() 
{
  var elementArray = $$('.logoImage');
  elementArray.each(function(item) {
    item.observe('mouseover',function(event){
      var element = Event.element(event);
      element.src = element.src.replace('_off','_on');
    });
    item.observe('mouseout',function(event){
      var element = Event.element(event);
      element.src = element.src.replace('_on','_off');
    });
  });

});