imageSet = new Array();

imageSet[0] = "<img src='/images/headers/header1.png' border='0'/>";
imageSet[1] = "<img src='/images/headers/header2.png' border='0'/>";
imageSet[2] = "<img src='/images/headers/header3.png' border='0'/>";
imageSet[3] = "<img src='/images/headers/header4.png' border='0'/>";
imageSet[4] = "<img src='/images/headers/header5.png' border='0'/>";

i = (Math.floor(Math.random()*imageSet.length));

document.write(imageSet[i]);