function resize_content() {
	var content = 'main';
	var sidebar = 'sidebar';
	if ($(sidebar) && $(sidebar).getHeight() > $(content).getHeight()) {
		$(content).style.height = $(sidebar).getHeight() + 'px';
	}
}
Event.observe(window, 'load', resize_content);
Event.observe(window, 'resize', resize_content);