img = new Array();
img[0] = "images/contents/index/mainimage1.jpg";
img[1] = "images/contents/index/mainimage2.jpg";
img[2] = "images/contents/index/mainimage3.jpg";
img[3] = "images/contents/index/mainimage4.jpg";
img[4] = "images/contents/index/mainimage5.jpg";
n = Math.floor(Math.random()*img.length);
document.write("<img src='"+img[n]+"' width='500' height='200' border='0' alt='' class='dispb' />");