function center (id) {
	var h = document.viewport.getHeight();
	var eh = $(id).getHeight();
	if (h >= eh) {
		var offset = (h - eh) / 2;
		$(id).setStyle({
			'top': offset + 'px'
		});
	}
}


Event.observe(window,'load',function (event) {
	center('container');
});

Event.observe(window,'resize',function (event) {
	center('container');
});