<div class="wrap">
<div class="main">
<div class="content"></div>
</div>
<div class="submain">2</div>
<div class="sidebar">3</div>
</div>

.wrap{width: 500px;border: 1px solid;overflow: hidden;}
.main{float: left;width: 100%;}
.content{height: 50px;margin: 0 150px;background-color: #f60;}
.submain{float: left;width: 150px;height: 50px;margin-left: -100%;background-color: #6f0;}
.sidebar{float: left;width: 150px;height: 50px;margin-left: -150px;background-color: #06f;}