Another good option if you like electronics is to use a stepper motor which is controlled by an Arduino. The following website has some stepper motors including geared steppers:
http://www.phidgets.com/products.php?category=23
You can also use a microstepper to increase the number of steps which can be individually controlled.
My brother is building something similar to control the motion of a line laser for 3d scanning using the David Laser Scanner software.
There lots of advice regarding the electronic design on the david laser scanning forum - e.g.
http://www.david-laserscanner.com/fo...pic.php?t=1999
Cheers,
Mark