con i float:
codice HTML:
<style type="text/css">
<!--
* {
margin:0;
padding:0;
}
#main {
}
#leftColumn {
float:left;
width:100px;
}
#rightColumn {
margin-left:100px;
width:auto;
}
#left {
width:50%;
float:left;
background-color:#CCCCFF
}
#right {
width:50%;
float:right;
background-color: #CC66FF
}
-->
</style>
</head>
<body>
<div id="main">
<div id="leftColumn">colonna da 100px</div>
<div id="rightColumn">
<div id="left">div sinistro</div>
<div id="right">div destro</div>
</div>
</div>
</body>
</html>