images = new Array(2);

images[0] = "<a href = 'http://www.coffeeparts.com/misc/group-seals.html'><img src='http://www.coffeeparts.com/banners/banner-groupseals.jpg' alt='Need a new seal?' border='0'></a>";

images[1] = "<a href = 'http://www.coffeeparts.com/misc/filter-baskets.html'><img src='http://www.coffeeparts.com/banners/banner-filterbaskets.jpg' alt='Want to go deeper?' border='0'></a>";

index = Math.floor(Math.random() * images.length);

document.write(images[index]);