var aryImages = new Array(2);

  aryImages[00] = "images/big/pic_house_05.jpg";
  aryImages[01] = "images/big/pic_house_02.jpg";
  aryImages[02] = "images/big/pic_house_03.jpg";
  aryImages[03] = "images/big/pic_shore_09.jpg";

  for (i=0; i < aryImages.length; i++) {
    var preload = new Image();
    preload.src = aryImages[i];
  }

  function swap(imgIndex) {
    document['imgMain'].src = aryImages[imgIndex];
  }