prova così CSS:
codice:
<style type="text/css">
<!--
.tdsoloadestra {
	border-top: 0px solid #999999;
	border-right: 1px solid #999999;
	border-bottom: 0px solid #999999;
	border-left: 0px solid #999999;
}
-->
</style>

HTML:
codice:
<td class="tdsoloadestra">contenuto td</td>
ciaux