<div id="content">
<div id="left">#left</div>
<div id="right">#right</div>
<div id="middle">#middle</div>
</div>

#content { width:700px; margin:auto; background:#FFF url(bg.png); border:1px #DCDCDC solid; text-align:left; }
#left{
float:left;
width:231px;
height:300px;
margin:0;
border-right:1px solid #EFEFEF;
}
#right{
float:right;
width:232px;
height:300px;
margin:0;
}
#middle{
border-right:1px solid #EFEFEF;
height:300px;
margin-left:232px;
margin-right:232px;
}