Despite them initially working, they seem to be causing some kind of problem within Community Server.
I'll see if I can't contact Ken Robertson to help me figure out what's going wrong.
FYI - when I mentioned that I was having problems getting photos from the gallery to show up and posted a link into Ken's post about Lightbox, he replied with this comment:
"Since the module was written by me and isn't directly supported by Telligent, would be easiest to just ask me the question directly. :) Can email me at ken AT qgyen DOT net.
To pull them directly from the gallery, you need to define the CSModule for the gallery mode, and then you use [photo:1234], 1234 being the PostID of the image, which you can get from the URL. IE, if the URL to view the image is http://devcow.com/photos/tech-ed_2006/picture944.aspx, then it would be [photo:944].
One of the other Telligent guys, Jim Martin created a way to add an image from the gallery using lightbox through the CS UI... have to find his module, but he has a little howto here: http://photogblogs.com/blogs/jim_martin/archive/2006/02/01/1484.aspx"
Thanks for getting back to me Ken. I'll send you some e-mail detailing my issues and when I have them all figured out I'll post the write-up here.
Basically - any post with a rel=lightbox tag is requiring a logged in user to view it. Then, once you're logged in, the Community Server engine shows me this error message: "Forum Gallery not found: 5 does not exist." When I posted a second Lightbox post to see if it was just a problem with my first post, the entire blog stopped loading. Stay tuned for more info as I have it.