window.addEvent('domready', function () {
	document.id(document).getElements('#header_menu > div').each(
function(el) {
		el.addEvent('mouseenter', function (event) {
			var height = document.id(this).getElements('li').length*40;
			document.id(this).getElement('ul').set('tween', {duration:500, link:'cancel', transition: Fx.Transitions.Sine}).tween('height', height);
		})
		.addEvent('mouseleave', function (event) {
			document.id(this).getElement('ul').set('tween', {duration:500, link:'cancel', transition: Fx.Transitions.Sine}).tween('height', 0);
		});
	});
});