images = new Array(4);
images[0] = "<img src='/images/header1.jpg'>";
images[1] = "<img src='/images/header2.jpg'>";
images[2] = "<img src='/images/header3.jpg'>";
images[3] = "<img src='/images/header4.jpg'>";
index = Math.floor(Math.random() * images.length);
document.write(images[index]);