Devantech CMPS03 compass sensor

hey guys,
im trying to program the Devantech CMPS03 sensor to read pwm values through the digital input, by measuring the pulses.
i have followed the instructions kindly posted in this thread:

and yet, i still get a reading of 0. im very unfamiliar with interrupts and hardware timers, so could anyone give me some hints on what to look for, maybe where i can set print statements to track the problem?

How is it wired? Perhaps you could post the suspect peice of code.