function get_random()
{

// random()*X) is the number of images
var ranNum= Math.floor(Math.random()*3);
return ranNum;
}
var whichImg=get_random();

function show_image() {

// Array(X) is the number of images
var img=new Array(3)
img[0]="homepageImages/Ir/39/mainBanner2.jpg";
img[1]="homepageImages/Ir/39/mainBanner2.jpg";
img[2]="homepageImages/Ir/39/mainBanner4.jpg";

document.write("<table background='");
document.write(img[whichImg]);
document.write("'>");
}