if (document.images) {

/* TOP */
var cnt01on = new Image();
cnt01on.src = "images/vol1index2.jpg";
var cnt01off = new Image();
cnt01off.src = "images/vol1index.jpg";

}

function On(name) {
  if (document.images) {
    document.images[name].src = eval(name + 'on.src');
  }
}

function Off(name) {
  if (document.images) {
    document.images[name].src = eval(name + 'off.src');
  }
}