The code below is the css for doing what you want.
<div style="width:80%;margin:0px auto;text-align:center;"><h1 style="float:left;">This is on the left</h1><h1 style="float:right;">This is on the right</h1></div>
<div style="clear:left;"> </div>
<p>As you can see about, it's done.</p>