<div style="width: 500px;">
 <div style="float: left; width: 200px;">Left Stuff</div>
 <div style="float: left; width: 100px;">Middle Stuff</div>
 <div style="float: left; width: 200px;">Right Stuff</div>
 <br style="clear: left;" />
</div>

เหมือนกัน

<style>
  .left{float:left; width:33%;}
</style>

<div class="left">...</div>
<div class="left">...</div>
<div class="left">...</div>

http://stackoverflow.com/questions/2156712/how-to-float-3-divs-side-by-side-using-css