HE Zhao wrote in to tell us about an open source Wii peripheral drum-kit project he's been working on:
I have recently developed Wii Drum High, a software integrates Wiimote, Nunchuk and Wii Balance Board to stimulate a complete drum set. Different gestures and joystick buttons result in correspondent drum sounds. I recorded some videos of real drummer playing with it, and it worked out pretty good.
The software, released under the GPL, is written in C# using Brian Peek's WiimoteLib API. Using the Visual C# Express development environment and WiimoteLib, you can make your own PC apps that use the Wiimote or Balance Board for input. Zhao's source is a good example to look at if you decide to head down this path, as is Peek's WiimoteLib guide on the coding4fun blog.