function swapNavOn(imageObj) {
  imageObj.src = imageObj.src.replace("_off", "_on");
}
function swapNavOff(imageObj) {
  imageObj.src = imageObj.src.replace("_on", "_off");
}
var preloadedImages = new Array()
function preloadImages(){
  for (i=0;i<preloadImages.arguments.length;i++){
    preloadedImages[i]=new Image()
    preloadedImages[i].src=preloadImages.arguments[i]
  }
}