Kyle,
The machine I saw at the college was an xy machine and was stepper driven. A servo machine would be quieter (this one had to be moved from it's original location because of the noise it made) but a bit more expensive.
The basics? A mechanism to move a fairly strong magnet under a table with a thin layer of sand and a ball bearing on top. Here are a couple of links
http://www.taomc.com/art/kinetic_scu..._i_and_ii.html
Here is a link to one of a different style (and a bit larger)
http://picasaweb.google.com/lh/photo..._kbTS9wZXpXexQ
Enjoy
Steve