function random_img(){
  var myimages=new Array()
  myimages[1]="images/ill_1.gif"
  myimages[2]="images/ill_2.gif"
  myimages[3]="images/ill_3.gif"
  myimages[4]="images/ill_4.gif"
  var ry=Math.floor(Math.random()*myimages.length)
  if (ry==0)
     ry=1
     document.write('<img src="'+myimages[ry]+'" border=0>')
}