var how_many_pics = 9;
var pic=Math.floor(Math.random()*how_many_pics)
pic +=1;

alt="";
banner="/images/HomeImg_" + pic + ".jpg";
width="792";
height="242";

document.write('<img src=\"' + banner + '\" width=');
document.write(width + ' height=' + height + ' ');
document.write('alt=\"' + alt + '\" border=0>');