var sScrollItem = 'divContent';
var iInterval = 20;
var iTimerId;

function setScroll(iAmount)
{
  stopScroll();

  document.getElementById(sScrollItem).scrollTop = document.getElementById(sScrollItem).scrollTop + iAmount;
  iTimerId = setTimeout("setScroll(" + iAmount + ")",iInterval);
}

function stopScroll()
{
  if (iTimerId) clearTimeout(iTimerId);
}