function top_image(){
img = new Array();
img[0] = "http://j-laf.org/00_special_img/top1.jpg";
img[1] = "http://j-laf.org/00_special_img/top2.jpg";
img[2] = "http://j-laf.org/00_special_img/top3.jpg";
img[3] = "http://j-laf.org/00_special_img/top4.jpg";
n = Math.floor(Math.random()*img.length);
document.write("<img src='"+img[n]+"' border='0'>");
}