You wouldn't use a resistor to lower the voltage, because then you have most of the power being dissipated in the resistor rather than the stepper motor. Much easier to just use a transformer or a 240V-rated stepper motor.
Well, normally you wouldn't draw power over that resistor, I was thinking more in the direction of using the power line as a "sense" pin for the stepper and power was provided properly via a transformer.
