Same here can't wait to see a Media Center Sideshow gadget. I'm really surprised to see how long it has taken to provide sideshow software for Windows Mobile.
Anyhow I'm really crossing my fingers that this spurs development.
Just installed Sideshow Dev Prev on Windows Mobile 6.1. No problems at all, the WMP gadget is functional, but the interface and layout leaves alot to be desired.
Since the WMP gadget is geared towards music playback. I much prefer the method I have been using. I use Remote Desktop to connect to the system, and use the actual Vista Media Center interface on the Windows Mobile Remote desktop session (via wireless) to control music playback, and even show slideshows of pictures on the Windows Mobile Device. (no good for video obviously).
Should mention that the Remote Desktop client included with Windows Mobile 5.x is nowhere near as capable/compatible with Vista as the Windows 6.x remote desktop client. Just my 2 cents.