var resizeTimeout;

function checkHeight() {
	var winHeight = document.documentElement.clientHeight;
	
	if (winHeight == 0) {
		winHeight = window.innerHeight;
	}
	
	clearTimeout(resizeTimeout);
	
	if (winHeight < 640) {
		if (document.getElementById('main').style.top!='320px') {
			resizeTimeout = setTimeout("document.getElementById('main').style.top='320px';",100);
		} 
	} else {
		if (document.getElementById('main').style.top!='50%') {
			resizeTimeout = setTimeout("document.getElementById('main').style.top='50%';",100);
		}
	}
	
}