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