WordPress MU

Hi

I'm trying to create a horizontal sub menu for my single posts. The idea behind the sub-menu is that it shows the child and grandchild options related to a parent category that the news story belongs. I've created the menu in css, http://fuximagazine.com/dev/commenu.html

And now I'm trying to create a widget that will show at the side of my news items. I've managed to get all the category options to show (please view: http://www.fuximagazine.com/film/2010/05/24/apichatpong-weerasethakul-wins-the-palme-dor-at-cannes/) But I would like the menu to just show that child and grandparent options related to the category that this particular item is posted in.

Does anybody know how I could change the following code to do this?

<div id="fuximenu">
	<ul>
	<li><a href="<?php echo single_cat_title(); ?></a></li>

 	<?php wp_list_categories('orderby=name&exlude=181&title_li=');
 	$this_category = get_category($cat);
 	if (get_category_children($this_category->cat_ID) != "") {
 		echo "<ul>";
	wp_list_categories('orderby=id&show_count=0&title_li=&use_desc_for_title=1&child_of='.$this_category->cat_ID);
 		echo "</ul>";
 	}
	?>

  	</ul>
	</div>

Would really appreciate any help, have been struggling with this for three and half days.