category based excerpt ( image ) navigation

Hi
I have severall problems with a category-based excerpt (=image) navigation. firstly i want the current category highlighted on the single.php. link: http://ba.goodandbad.net/dasmoebel (current category is Projekte). The problem is: when i am on the single.php here the class current-cat should be added to the wp-list-categories (li Projekte).

Here es the code for the excerpt:

<?php query_posts('category_name=Projekte&posts_per_page=-1'); ?>
            <?php while (have_posts()) : the_post(); ?>
            	<div class="column grid_1">
            		<div id="ex" rel="post-<?php the_ID(); ?>" onmouseover="this.style.opacity=1;this.filters.alpha.opacity=100"onmouseout="this.style.opacity=0.5;this.filters.alpha.opacity=50">
             		<?php the_excerpt(); ?>
            		</div>
           		</div>
            <?php endwhile; ?>