Fancybox with magic fields. (Custom fields)

I am having an issue trying to get fancybox to work on my wordpress site. The site uses magic fields to display a gallery of images. I use echo get_image to display the thumbnail that I have uploaded to the custom field ‘port_thumb’ in each post. I want it so that when I click on the thumbnail a larger image will open up in a fancybox on that same page. This is the code for the thumbnails.

<li><?php echo get_image('port_thumb');?></li>

How do I create the link for fancybox to the above code? Below is the code that i currently have directly above the ‘port_thumb’. ‘fb_zoom’ is another custom field that points in the direction for the larger images. Right now all this does is open the larger image in a different page

<a class="fancybox" rel="group" href="<?php bloginfo('template_directory'); ?
>/images/images/zoom/<?php echo get('fb_zoom'); ?>">

I have tried following the guide on http://fancybox.net/howto but I am having a hard time understanding what to do when using PHP and magic fields.