<div id="box1">

<div id="left1"></div>

<div id="right1"></div>

</div>

#box1{width:100%;height:600px;position:relative;}

#left1{margin-right:200px;border:1px solid red;height:100%;}

#right1{width:200px;height:100%;position:absolute;top:0px;right:0px;border:1px solid blue;}