div布局整理

======================上下两行四个区域布局=====================

其中:
div{
	border:0px;
	margin:0px;
}

<div style="clear:both;width:100%;">
   <div style="width:50%;float:left;">left1</div>
   <div style="width:50%;float:right;">right1</div>
</div>
<div style="clear:both;width:100%;">
   <div style="width:50%;float:left;">left2</div>
   <div style="width:50%;float:right;">right2</div>
</div>