Step 2: Working principle
The driving motor part is basically untouched. The speed of a floppy disc drive is to slow. Therefore the motor driver need to be modified to make the motor turn faster.
Parts of the other motor can be used to build a generator. Using a dc brushless motor we get three phase current, see http://en.wikipedia.org/wiki/Three-phase_electric_power . The three phases are rectified with three diodes and the resulting voltage can be used to power the pov circuit.
The coils of the generator need to spin with the pov pcb. Therefore the magnets need to be mounted onto the static pcb of the motor and the star with the coils onto the spindle of the motor.