function AnimateOpacity(elementId, duration, showElement)
{
    var element = DOM.get(elementId);

    if (element.style.display == 'none')
    {
        element.style.display = '';
    }

    var anim;
    var finalOpacity;

    if(showElement)
    {
        anim = new YAHOO.util.Anim(element, { opacity: { from: 0, to: 1} }, duration, YAHOO.util.Easing.backIn);
        finalOpacity = 1;
    }
    else
    {
        anim = new YAHOO.util.Anim(element, { opacity: { from: 1, to: 0} }, duration, YAHOO.util.Easing.backIn);
        finalOpacity = 0;
    }

    var f = function ()
    {
        anim.onComplete.unsubscribe(f);
        element.style.opacity = finalOpacity;
    }
    anim.onComplete.subscribe(f, anim, true);
    
    anim.animate();
}