window.onload = rotate;

var thisAd = 0;

function rotate() {
var adImages = new Array("banner4.jpg", "banner5.jpg", "banner6.jpg", "banner7.jpg");


thisAd++;
	if (thisAd === adImages.length) {
		thisAd = 0;
	}
	document.getElementById("adBanner").src = 
	adImages[thisAd];

	setTimeout(rotate, 5 * 1000);
}