I've released my Arduino satellite tracking project, entitled qrpTracker.
qrpTracker includes a library that is a port of the long-standing Plan13 satellite tracking algorithm, and another library that stores and retrieves Keplerian elements. (These are the basic who, what where of satellite tracking.) There is also a separate library to control a FT-817 amateur radio through a hardware serial port.
On its own, the Arduino with an ATMega328 at 16 MHz can store data for about 13 satellites in EEPROM and can process one satellite's location every 10ms. There's lots of programming space left over after the Plan13 and EEPROM code.
Unfortunately, this BB software will not let me post links, so I can't direct you to the project website, introductory video or even to the googlecode repository. It says I can post links after one posting without links, so if anyone's interested, I'll do that as a follow-up.