var source = 0;
var replacement = 1;

function createRollOver(originalImage, replacementImage) {
  var imageArray = new Array;
  imageArray[source] = new Image;
  imageArray[source].src = originalImage;
  imageArray[replacement] = new Image;
  imageArray[replacement].src = replacementImage;
  return imageArray;
}

function roll(targetImage, displayImage) {
  targetImage.src = displayImage.src;
}