<style type="text/css">.cpopup {position:absolute;top:0px;left:0px;width:0%}div > div.cpopup {position:fixed;}</style>       
<!--[if gte IE 5.5]><![if lt IE 8]><style type="text/css">div#upopup {width:expression(((ignoreMe=(document.documentElement.clientWidth?document.documentElement.clientWidth:document.body.clientWidth))<200?200:        ignoreMe)+'px');  position:absolute;top:expression((ignoreMe2=document.documentElement.scrollTop?document.documentElement.scrollTop:document.body.scrollTop)+'px');     
left:expression((ignoreMe=document.documentElement.scrollLeft?document.documentElement.scrollLeft:document.body.scrollLeft)+'px');  }</style><![endif]><![endif]-->       
<div id="ppopup">       
<div class="cpopup" id="upopup">       
<!--START-->       
Тут ставят окно или скрип,  после чего оно будет плавать.       
<!--END-->       
</div></div>       
<script type="text/javascript">document.getElementById("ppopup").style.height=document.getElementById("upopup").offsetHeight+'px';  </script>