Oops, forgot the clip values that NS4 needs. Don't ask me why, lol.
<STYLE type="text/css"> <!--
#behind {
position:absolute;
background:white;
layer-background-color: White;
top:100px;
left:0px;
width:200px;
height:100px;
clip:rect(0,200,100,0);
}
-->
</STYLE>
Try that.