ผมใช้แบบนี้ครับ
#floating_banner_bottom {
   text-align: center;
   width: 200px;
   bottom: 0px;
   margin-bottom: 0px;
   height: 500px;
   position: fixed;
   z-index: 100;
   right: 0;
   _position:absolute;
   _top:expression(document.body.scrollTop document.body.clientHeight-this.clientHeight);
}

<div id="floating_banner_bottom">.....</div>

<script type="text/javascript">
var name = "#float_banner";
$(name).css("top",(($(window).height())-180) "px");
var locateY= null; 
$(function(){
   locateY=parseInt($(name).css("top").replace("px",""));
   $(window).scroll(function(){
      offset=locateY $(document).scrollTop() "px";
      $(name).animate({top:offset},{duration:1000,queue:false});
   });
});
</script>