用DIV怎么样布个3行2列的版面

CSS
#maiBox{width:1003px;marigh:0 auto; overflow:auto;}
.divright,.divleft{float:left;width:499px; height:100px;}
.divright{float:right;}

HTML
<div id="mainBox">
<div class="divleft">1</div>
<div class="divright">2</div>
<div class="divleft">3</div>
<div class="divright">4</div>
<div class="divleft">5</div>
<div class="divright">6</div>
</div>