function threeColumn() {
	var mainDiv = document.getElementById('content');
	var headerDiv = document.getElementById('header');
	var subnavDiv = document.getElementById('subnav');

	var y = headerDiv.offsetHeight;

	mainDiv.style.height = 'auto';
	var x = mainDiv.offsetHeight;
	mainDiv.style.height = x + "px";
	subnavDiv.style.height = (x - y) + "px";
}