var banner_options = ["images/top-banners/banner-images-1.jpg",
			"images/top-banners/banner-images-2.jpg",
			"images/top-banners/banner-images-3.jpg",
			"images/top-banners/banner-images-4.jpg",
			"images/top-banners/banner-images-5.jpg",
			];

function set_banner_image(){
	document.images.top_banner_image.src = banner_options[Math.floor(Math.random()*5)];
}

set_banner_image();