var scrolling;
function startScroll(id, dir) {
  var speed = 0;
  if (dir == 'up') {
    speed = -3;
  } else if(dir == 'down') {
    speed = 3;
  }
  performScroll(id, speed);
}
function performScroll(id, speed) {
  var el = document.getElementById(id);
  el.scrollTop += speed;
  scrolling = setTimeout("performScroll('" + id + "', " + speed + ")", 20);
}
function stopScroll() {
  clearTimeout(scrolling);
}