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

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

if(StartScroll())
{
  if(document.getElementById('chatbox').scrollTop == (document.getElementById('chatbox').scrollHeight - document.getElementById('chatbox').offsetHeight))
    setTimeout("clearInterval(ScrollDown)", 1000);
}