Event.observe(window, 'load', function()
{
    var tabs = document.getElementsByClassName("trhighlight");
    
    tabs.each(function(tab)
    {
        
        Event.observe(tab, 'mouseover', function()
            {
                Element.addClassName($(tab), 'highlight');
            }
        );
        
        Event.observe(tab, 'mouseout', function()
            {
                Element.removeClassName($(tab), 'highlight');
            }
        );
    });
    
});