function toggleMenu(el, over)
{
    if (over) {
        Element.addClassName(el, 'over');
    }
    else {
        Element.removeClassName(el, 'over');
    }
}
button = {
show: function(elem) {
document.getElementById(elem).style.visibility = 'visible';
},
hide: function(elem) {
document.getElementById(elem).style.visibility = 'hidden';
}
}