if (document.images) {

  // new button
  bookOn = new Image();
  bookOn.src = "images/nav/book-ro.gif"

  bookOff = new Image();
  bookOff.src = "images/nav/book.gif"

  // new button
  authorOn = new Image();
  authorOn.src = "images/nav/author-ro.gif"

  authorOff = new Image();
  authorOff.src = "images/nav/author.gif"

  // new button
  excerptOn = new Image();
  excerptOn.src = "images/nav/excerpt-ro.gif"

  excerptOff = new Image();
  excerptOff.src = "images/nav/excerpt.gif"

  // new button
  buyOn = new Image();
  buyOn.src = "images/nav/buy-ro.gif"

  buyOff = new Image();
  buyOff.src = "images/nav/buy.gif"

  // new button
  mediaOn = new Image();
  mediaOn.src = "images/nav/media-ro.gif"

  mediaOff = new Image();
  mediaOff.src = "images/nav/media.gif"

}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}