How to display categories of the Custom Taxonomy

Hello,
I have custom post type created – ‘Portfolio’ which is my home page and I want to display custom categories (‘Galleries’) of this post type instead of default post categories but don’t know how to achieve this. I am using the following code:

<div id="filtering-nav">
		<a href="#"><span>Filter</span></a>

<ul>
<li><a href="#all">All</a></li>
		<?php
		$args=array( 'orderby' => 'name' );
		$galleries=get_categories($args);
		foreach($galleries as $gallery) {  ?>

<li><a>category_nicename; ?>" class="<?php echo $gallery->category_nicename; ?>"><?php echo $gallery->name; ?></a></li>
		<?php } ?>
		</ul>
		<div class="clearfix"></div>
</div>

…but it doesn’t work at all!!
Hope that someone can help me solve the problem. I am completely new to WordPress.

Thanks in advance!