The great people over at Solarbotics.com put together a Solar Xylophone kit that allows you to easily purchase all the parts you will need for one of the solar engine circuits. Solarbotics is a really nice site, so if you haven't checked it out already, head on over there. Thanks guys!
Lastly, if there is anyone out there working on building a solar xylophone I'd really like it if you could send some pictures my way. I'd love to check them out!