pic = new Array(3);
pic[0] = '1.jpg';
pic[1] = '2.jpg';
pic[2] = '3.jpg';
pic[3] = '4.jpg';
idx = Math.floor(Math.random() * pic.length);
document.write("<a href=./pic/index.htm><IMG border=1 width=170 height=160 src=./"+pic[idx]+"></a>");