function changeImage(layer,imgName,imgObj) {
   if (document.images) {
      if (document.layers && layer!=null) eval('document.'+layer+'.document.images["'+imgName+'"].src = '+imgObj+'.src')
      else document.images[imgName].src = eval(imgObj+".src")
   }
}

function preload(imgObj,imgSrc) {
  if (document.images) {
      eval(imgObj+' = new Image()')
      eval(imgObj+'.src = "'+imgSrc+'"')
   }
}