Another option is the Linistepper clock project
techref.massmind.org/techref/io/stepper/linistep/LiniClock/index.htm
or telescope mount
techref.massmind.org/techref/io/stepper/linistep/equatorial.htm
Each of those provide a stepper drive with the clock source built in. You can rig up your own switch to the direction input to change the direction manually.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)