Stepper Motor Igoe Example

Hi, i am new to electronics, but i tried to get a good start with the "Physical Computing" book. I want to do the bipolar stepper motor example with h-bridge (it's also online: ) with arduino, but i have some questions left: - what all do i connect to ground, since i am using a external power supply for the motor: only the arduino ground, or also the external power supply ground (do i have to use it at all, or only its positive connection)? - i have got a 5017-935 stepper motor from scotts valley, it tells me dc 8.4 V, but i downloaded also its data sheet, and this tells me that its phase voltage should be 6 VDC??? - the code-example for the arduino tells me to use outputs 8,9,10,13 on the arduino(=inputs in h-bridge). Do they correspondend to the wires 1, 2, 3, 4 (yellow, white, blue, red) from the motor, that go to the h-bridge-outputs (that means input 1 in h-bridge should be d8 at arduino, and output 1 in h-bridge the yellow wire)

thanks for any help