url = new Array(2);
image = new Array(2);

url[0] = "http://shop.seattlemarathon.org";
image[0] = "images/main/promobox_gear.png";


url[1] = "http://www.seattlemarathon.org/10k/10kregister.php";
image[1] = "images/main/promobox_10k.png";


//calculate a random index
index = Math.floor(Math.random() * url.length);
document.write("<a href=\"" + url[index] + "\"><img src=\"" + image[index] + "\" /></a>\n");