x = 55; // マウスと画像の縦方向の距離
y = 25; // マウスと画像の横方向の距離
flag = false;
window.document.onmousemove = dragImg;
window.document.onmouseup = dragOff;
function dragOn(n) {
  flag = true; 
  imgName = n;
}
function dragOff() {
  flag = false;
}
function dragImg() {
  if(!flag) return;
  document.images[imgName].style.top = event.y - y;
  document.images[imgName].style.left = event.x - x;
  return false;
}

(new Image()).src = "menubar2.gif";
(new Image()).src = "menubar2_h.gif";