var cb = document.getElementById('chatbox');
function ScrollDown()
{
  cb.scrollTop = cb.scrollHeight - cb.offsetHeight;
}

function StartScroll()
{
  ScrollDown = setInterval("ScrollDown();", 10);
}

if(StartScroll())
{
  if(cb.scrollTop == (cb.scrollHeight - cb.offsetHeight))
    setTimeout("clearInterval(ScrollDown)", 1000);
}