Some steppers are 1.8 degree, 200 steps. Some are not...
The Epson steppers might be 3.6 degree, 100 steps.
You will need two H bridges to control a bipolar stepper, one for each coil.
What driver are you using, where is the schematic?
Is this it: http://arduino.cc/en/Reference/StepperBipolarCircuit
In this case the L293D is a dual
If it just vibrates then you have some motor wires mixed up...
Or you might be trying to move it too fast with too little current.
Try reversing one coil and slow it down...