<style type="text/css">
<!--
#left {
background-color:#0000CC;float:left;width:100px;}
#right {
background-color:#000000;float:right;width:200px;}
#contain {width:300px;height:400px;clear:both;}

-->
</style>
<div id="contain">
<div id="left"> <br/ ><br/ ><br/ ><br/ ><br/ > </div>
    
<div id="right"><br/ ><br/ ><br/ ><br/ ><br/ ><br/ ><br/ >    
</div>
</div>


<script type="text/javascript">
document.getElementById("left").style.height=document.getElementById("right").scrollHeight+"px"
</script>