How about :-

<style type="text/css">
#disp_<?php echo $disp; ?>{
/*
your "active" css goes here
*/
}
</style>

......

<ul id="menu">
<li id="disp_comments"><a href=".....">....</a></li>
<li id="disp_msgform"><a href=".....">....</a></li>
<li id="disp_arcdir"><a href=".....">....</a></li>

...
</ul>

¥

Thanks, I'll give it a spin...
Look's logical :)

Perfect... had to frig around with some existing CSS, but other than that, you have done it again.