Center text within table cell

Hi-

I am trying to align text within the <dt> tag of a table.  The text also functions as a link.  I have set the CSS to:

.caption a {

          text-align:center;

          font-family:"Arial Unicode MS";

          font-size:18px;

          color:#FFF;

}

HTML code:

<td class="caption"><a href="#">Transportation</a></td>

Site:

http://www.sbaisden.com/portfolio.html

I have attempted several troubleshooting methods but nothing seems to work.  Any ideas are greatly appreciated.  Thanks!