var last_id='';

function SwapImage(id)
{
    btn_id = eval(id + 1);

    image_div = document.getElementById('ad_image_div');
    btn = document.getElementById('btn_0'+btn_id);
    last_btn = document.getElementById('btn_0'+eval(last_id+1));


    image_div.innerHTML = '<a href="'+ad_links[id] +'"'+ ad_clicks[id] +'>'+ '<img src="' + ad_images[id] + '" border=0></a>';

    // only change if clicking a different number
    if (last_id != id)
    {
        btn.src="images/adBtn_0"+btn_id+"_over.jpg";
        last_btn.src="images/adBtn_0"+eval(last_id+1)+".jpg";
    }

    last_id = id;

}