/*parameters for this function is an image id tag followed by a list of images
like randImg('images/banner1.jpg', 'images/banner2.jpg', 'images/banner3.jpg'); 
only use this script AFTER the image tag occurs in html code*/
function randImg(){
var list = randImg.arguments;
var index = Math.floor((Math.random()*(list.length-1))+1);
document.getElementById(list[0]).src = list[index];
}