Wow . . . just wow! Johnny Chung Lee is really clever. He has come up with a complete electronic whiteboard system that you can make yourself really cheaply. You can find the hardware and software instructions, including a very popular YouTube video and the software downloads on his Wii Project page here. You can also view a great demo of his new projects on TEDBlog here. (I tried embedding the video here using the code they give on TEDBlog, but for some reason Blogger didn't allow the video content to load.)
The only limits to what we might be able to use this for in museums are the bounds of our imagination.