function centerVertically() {
	var heightMain = parseInt($('main').getStyle('height'));
	
	if(document.documentElement.clientHeight) {
		var heightBrowser = parseInt(document.documentElement.clientHeight);
	} else {
		// for IE6
		var heightBrowser = parseInt(document.body.clientHeight);
	}

	if(heightBrowser - heightMain >= 30) {
		var marginTop = (heightBrowser - heightMain)/2;
		$('main').setStyle('margin-top', marginTop + 'px');
	} else {
		$('main').setStyle('margin-top', '15px');
	}
}

// run centerVertically as soon as the page is ready
window.addEvent('domready', centerVertically);
window.addEvent('resize', centerVertically);