Hi Chris, The only available option for picture galleries here on WordPress.com is the native Gallery feature, which you can set up to open images on a separate attachment page. http://en.support.wordpress.com/images/gallery/ Also, http://gammagirl.wordpress.com/2008/07/27/not-the-official-wordpresscom-gallery-faq/
One more possible option is to use a flickr slideshow, which can be opened to full screen from within the slideshow. You need to enable Auto Embed on your Media Settings page and then copy and paste the slideshow link from flickr on its own line in your post or page, making sure the link ends in "/show/" and the link is not highlighted as a link (using the "unlink" button if necessary).
There is also the CSS style for "thickbox" which is a workaround, but not easy to implement.
No other options for a picture gallery are presently available.