The method I use uses JavaScript in the <head>
Code:
<script type="text/javascript">
window.onload = function() {
var b1 = document.getElementById("columnone");
var b2 = document.getElementById("columntwo");
var m = Math.max(b1.offsetHeight, b2.offsetHeight);
if (b1.offsetHeight!=m) b1.style.height=m+'px';
if (b2.offsetHeight!=m) b2.style.height=m+'px';
}
</script>