style sheet/design issue

I have a web site (netleets.com) that utilizes a style sheet to organize article columns. There are 3 columns on each page. As new articles are added a "new row" element is used to push every 4th article down to a new row. My problem is that every time I add a new article, I have to retag all of the preexisting articles so that every 4th is pushed down to a new row. Is there a way to automate this process in any way? For example: See "row-start" below in the first and 4th section.

<div class="story-ref row-start important">
<h3><a href="2008/10/ciscovpn.htm">Cisco releases bogus VPN client</a></h3>
<p class="standfirst">But on the brite side, you do get 12 new songs for your
iPod</p>
<p class="stamp"> <span class="date">Oct 11</span></p>
</div>

<div class="story-ref important" style="width: 175px; height: 72px">
<h3><a href="2008/10/malware.htm">You've got malware</a></h3>
<p class="standfirst">Yes you. According to Google</p>
<p class="stamp"> <span class="date">Oct 11</span></p>
</div>

<div class="story-ref">
<h3><a href="2008/10/palin.htm">Victim of the month:Sarah Palin 9/17/2008</a></h3>
<p class="standfirst">You too can own Sarah's email if you can guess her zip
code. Hint, hint, Mr. Google already knows</p>
<p class="stamp"> <span class="date">Oct 09</span></p>
</div>


<div class="story-ref row-start" style="width: 175px; height: 140px">
<h3><a href="http://www.foxnews.com/story/0,2933,435681,00.html">World Bank
servers compromised for more than a year</a></h3>
<p class="standfirst">&quot;They were downloading everything and anything. They
[intruders] had full access.&quot;</p>
<p class="stamp"> <span class="date">Oct 11</span></p>
</div>


If I add a new article, I have to rearage all of the the above/