function setHeight(id1, id2) {

    height1= getElementHeight(id1);
    height2= getElementHeight(id2);

    if (height2 > height1) {

        document.getElementById(id1).style.height= height2 + 'px';
    }
}

function getElementHeight(id) {

    var elt= document.getElementById(id);

    return elt.style.pixelHeight || elt.offsetHeight;
}

function vpHeight() {  
    return window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;  
}