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) {  
    btn_1 = newImage("images/b01a.gif");    
    btn_2 = newImage("images/b02a.gif");    
    btn_3 = newImage("images/b03a.gif");    
    btn_4 = newImage("images/b04a.gif");    
    btn_5 = newImage("images/b05a.gif");    
    btn_6 = newImage("images/b06a.gif");    
    btn_7 = newImage("images/b07a.gif");    
    btn_8 = newImage("images/b08a.gif");    
    preloadFlag = true;
  }
}

preloadImages();