Philip:

Measure continuity with an ohm meter.  You will probably discover that you have
 two windings.  If so, this is a two-phase bipolar motor.  If all four wires
are interconnected, this is a three-phase unipolar motor.  In the latter case,
find the common wire (the one with the same DC resistance each of the remaining
 three).

If it's bipolar, you need two H bridor each winding.  Now use the four
bits to drive each winding forward or reverse polarity.

If it's three-phase, connect common to +12V and ground the three coils one at
a time like this:
0001
0010
0100
and repeat.

You can experiment with phase switching sequences by hand.  Get a bunch of
clip leads and wire up the motor for each phase pattern one at a time.  When
you energized each new phase pattern, the motor should "clunk" and advance a
little bit.

- Mark Sullivan -