var iImg = 1;
var totalImages = 0;

function showPreview(images) {
    if (iImg >= totalImages) {
	    iImg = 0;
    }

    var src = images.split(",");
    totalImages = src.length;

    setTimeout("switchAd('" + src[iImg] + "')", 1500);
}

function switchAd(imageURL) {
    document.getElementById('theImage').src = imageURL; 
	iImg++;
}