I'm running a Linux Second Life client that features dynamic shadows, multiple spotlights and projected textures. It's awesome - have a look to media below.

The viewer is still buggy but it didn't need patches, and it wasn't very difficult to build it from Linden Lab 'render-pipeline' codebranch, so I'm pretty sure that someone else could do the same for Windows and Mac OS X.
If you a friend that can do this for you, or know a developer you trust, ask them to build a shadows viewer for you. I'd be glad to help even if I'm not a competent developer - feel free to contact me in-world.

Photos:
http://www.flickr.com/photos/opensourceobscure
Videos:
http://www.youtube.com/user/opensourceobscure
(recent stuff is about shadows only)