function setTall() {
    if (document.getElementById) {

        var nav = document.getElementById('nav');
        var content = document.getElementById('content');

        if (nav && content) {
                if (nav.offsetHeight > content.offsetHeight) {
                        content.style.height = (nav.offsetHeight) + 'px';
                }
        }
    }
}

window.onload = function() {
    setTall();
}

window.onresize = function() {
    setTall();
}