function newImage(arg) {
  if (document.images) {
    rslt = new Image();
    rslt.src = arg;
    return rslt;
  }
}

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

var preloadFlag = false;
function preloadImages() {
  if (document.images) {
    b1_over = newImage("i/b1-over.jpg");
    b2_over = newImage("i/b2-over.jpg");
    b3_over = newImage("i/b3-over.jpg");
    b4_over = newImage("i/b4-over.jpg");
    b5_over = newImage("i/b5-over.jpg");
    b6_over = newImage("i/b6-over.jpg");
    preloadFlag = true;
  }
}