<div style="width: 100%;">
<div style="float: left; width: 33%;">Row 1 - Cell 1</div>
<div style="float: left; width: 34%;">Row 1 - Cell 2</div>
<div style="float: left; width: 33%;">Row 1 - Cell 3</div>
</div>
<div style="clear: left; width: 100%;">
Row 2 - Cell 1
</div>