var TzHoldcoAd = function() {
    var BB     = document.getElementById('cow_bix_box_swf');
    var Expand = document.getElementById('cow_rollover');

    BB.onmouseover = function() {
        Expand.style.display = 'block';
        BB.style.display = 'none';
    }

    Expand.onmouseout = function() {
        Expand.style.display = 'none';
        BB.style.display = 'block';
    }
}();