var imgs = new Array("images/banner_home_1.jpg", "images/banner_home_2.jpg", "images/banner_home_3.jpg", "images/banner_home_4.jpg", "images/banner_home_5.jpg");

function Images() {
var image = this.imgs[(Math.floor((Math.random() * imgs.length)))];
document.write('<a href="produtos.asp"><img src="' + image + '" alt="SHIGA" width="770" height="237" border="0"></a>');
}