function toggle() {
    if (document.all&&document.getElementById) {
        var aParents = $A(document.getElementsByClassName('parent'));
        
        aParents.each(function(node) {
            Event.observe(node, 'mouseover', function() {
                node.addClassName('hover'); 
            });
            Event.observe(node, 'mouseout', function() {
                node.removeClassName('hover'); 
            });
        });
    }
}
Event.observe(window, 'load', toggle);