images = new Array();

images[0] = '<img src="/images/headers/00.jpg" />';
images[1] = '<img src="/images/headers/01.jpg" />';
images[2] = '<img src="/images/headers/02.jpg" />';
images[3] = '<img src="/images/headers/03.jpg" />';
images[4] = '<img src="/images/headers/04.jpg" />';
images[5] = '<img src="/images/headers/05.jpg" />';

index = Math.floor(Math.random() * images.length);
document.write(images[index]);