<style>
.parent
{
width:100%;
}
.left
{
width:140px;
float:left;
}
.center
{
margin-left:150px;
margin-right:110px;
}
.right
{
width:100px;
float:right;
}
.clear
{
clear:both;
}
</style>
<div class="parent"><div class="left"></div><div class="center"></div><div class="right"></div><div class="clear"></div></div>

–注意：
当然如上布局时在ff,ie8下时，parent底部会产生空白。解决办法修改.parent，添加overflow:hidden;