Lacking a label on the motor, you can generally tell the two apart by feel when no power is applied. You can also distinguish between the two varieties with an ohmmeter. Center-tapped windings are used in unipolar permanent magnet motors.
Stepping motors come in a wide range of angular resolution.
The coarsest motors typically turn 90 degrees per step, while high resolution permanent magnet motors are commonly able to handle 1.8 or even 0.72 degrees per step. With an appropriate controller, most permanent magnet and hybrid motors can be run in half-steps, and some controllers can handle smaller fractional steps or microsteps. If your motor has three windings, typically connected as shown in the schematic diagram in Figure 1.1, with one terminal common to all windings, it is most likely a variable reluctance stepping motor. In use, the common wire typically goes to the positive supply and the windings are energized in sequence. The cross section shown in Figure 1.1 is of 30 degree per step variable reluctance motor.