shift register + h-bridge + bipolar motor = noise?

i've got a shift register connnected to an h-bridge connected to a 4-pin stepper motor. further down the shift register there are some LEDs. When I try to power the stepper motor, the LEDs further down flicker about in nonsensical ways. the shift register, or maybe the whole board seems to freak out. i have an ir sensor connected that is being triggered when it shouldn't be during the freak out. does anyone know why that would happen?

just having the shift register + h-bridge disconnected from the stepper motor doesn't cause this. i'm following the typical Physical Computing method for controlling bipolar stepper motors. i haven't been able to figure out what the order of the 4 pins is.

any tips on dealing with this? is it about isolating that noise, or am i just doing something very wrong?

Circuit diagram?
Is your power supply up to the job?
Do the LEDs flicker if you run the software, but leave the motor disconnected?

i'm following the typical Physical Computing method for controlling bipolar stepper motors

What does this mean, please?

Shift register connected like this:

Except four of the outputs from the shift register go to the h-bridge like this:
http://www.tigoe.net/pcomp/img/stepper-bipolar-hbridge.jpg

In the second diagram, "To microcontroller outputs ..." are connected to the shift register outputs instead.

i've got a 24VDC 400mA adapter. Should be plenty right? I've tried ones with less voltage, same results until it stops running the motor altogether.

The LEDs don't flicker if I run the software with the motor disconnected.

The "Physical Computing method" I was referring to is that stepper motor/h-bridge diagram from the book Physical Computing. This one, from the authors website, is the same, and the one I linked to above:
http://www.tigoe.net/pcomp/img/stepper-bipolar-hbridge.jpg

Sorry to be so vague about that.

on a whim i added 10K resistors on pins 2 and 4 (or maybe 1 and 3) of the stepper motor, and everything worked as it should, except the resistors started smelling and turning black after a minute or so. so... stronger resistors?