function getWindowHeight() 
{
  var windowHeight = 0;
  if (typeof(window.innerHeight) == 'number') 
    { windowHeight = window.innerHeight; }
  else 
    {
      if (document.documentElement && document.documentElement.clientHeight)
        { windowHeight = document.documentElement.clientHeight;	}
      else
        {
          if (document.body && document.body.clientHeight)
            {windowHeight = document.body.clientHeight; }
        }
    };
  return windowHeight;
}

function setFooter()
{
  if (document.getElementById) 
    {
      var windowHeight = getWindowHeight();
      if (windowHeight > 0)
        {
           var contentHeight = document.getElementById('main').offsetHeight - document.getElementById('footer').offsetHeight;
           var footerElement = document.getElementById('footer');
           var footerHeight  = footerElement.offsetHeight;
           if (windowHeight - (contentHeight + footerHeight) >= 0)
             { footerElement.style.top = (windowHeight - (contentHeight + footerHeight)) + 'px'; }
          else
             { footerElement.style.top = '0px'; }
         }
     } 
}