Thumbnails in the sidebar

Hi

I’m using a plugin to help me with my custom tags, like header images and such like for posts, but I want to make a thumbnail selection in my sidebar based on a custom tag I have called in simply as <?php echo c2c_get_custom('thumbnail'); ?>

Is it possible to get this from my RSS feed?

I’m not really looking to make a gallery, rather list some thumbnails like the flickr plugin and have them link to respective entries. As seen on my site: http://www.dadako.com

Any help would be greatly received, thanks.