var maxHeight = function(classname) {
	var divs = document.getElements('div.' + classname);
	var max = 0;
	divs.each(
			function(div) {
			max = Math.max(max, div.getSize().size.y);
			}
	);
	divs.setStyle('height', max);
	return max;
}
window.addEvent('load', function() {
	maxHeight('equal');
	maxHeight.delay(500, maxHeight, 'equal');
}
);

function thisheight()
{
	var top=document.getElementById("top").offsetTop;
	var bottom=document.getElementById("bottom").offsetTop;
	var height=bottom-top;
	
	document.getElementById("col1").style.height=height+'px';
	document.getElementById("col2").style.height=height+'px';
	document.getElementById("col3").style.height=height+'px';
}