first-letter при помощи JavaScript. replace.

<div id="uOnline">$ONLINE_USERS_LIST$</div>

<div id="uOnline">
<a class="groupUser" href="javascript://" rel="nofollow" onclick="window.open('http://likbezz.ru/index/8-801','up801','scrollbars=1,top=0,left=0,resizable=1,width=680,height=350');return false;">snayper</a>, <a class="groupUser" href="javascript://" rel="nofollow" onclick="window.open('http://likbezz.ru/index/8-784','up784','scrollbars=1,top=0,left=0,resizable=1,width=680,height=350');return false;">Solyt</a>, <a class="groupAdmin" href="javascript://" rel="nofollow" onclick="window.open('http://likbezz.ru/index/8-1','up1','scrollbars=1,top=0,left=0,resizable=1,width=680,height=350');return false;">likbezz</a>
</div>

<script type="text/javascript">
$('#uOnline a').each(function(i){
$(this).html($(this).html().replace(/([^\t])([^\t]+)/i,"<b style='color:#F00;'>$1</b>"+"$2"));
});
</script>

<style type="text/css">
#uOnline a b{color:#F00;text-transform:uppercase;}
</style>

<script type="text/javascript">
$('#uOnline a').each(function(i){
$(this).html($(this).html().replace(/([^\t])([^\t]+)/i,"<b>$1</b>"+"$2"));
});
</script>