Just in regards to the circuit;
One pulse from the PIC will result in a 1/2 step on the motor, and it will hold there awaiting the next step. Note C1 and R1 - 3, they form the chopper circuit. This is a form of current control for the motor, to allow the input voltage to be greater than that of what the motor is rated for. To find out how much current the stepper can handle, read the datasheet, or divide its nominal voltage by the resistance of the coil. The ammeter in this circuit was used to ascertain the values of R1 and R2, as the supply voltage was 24VDC and the stepper nominal voltage is 12V. Without chopper control the motor will draw too much current, so R1 and R2 are increased in value until the current being consumed by the motor is the same to that as if it were only connected to 12VDC (~.05A).