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) {
  m1a = newImage("image/menu01a.gif");
  m2a = newImage("image/menu02a.gif");
  m3a = newImage("image/menu03a.gif");
  m4a = newImage("image/menu04a.gif");
  preloadFlag = true;
 }
}