Check out page TM-177 of the FSM:
http://www.nicoclub.com/manuals/Pathfin ... der/TM.pdf
TM-20 has some info where to find the switches.
As attofarad mentioned, there's a solenoid that controls the ability to shift out of park when the brake pedal is depressed. There's also a park position switch on the shifter assembly that's in the circuit. All three will need to be checked.
Overall design hasn't changed much. I had the same problem on my 04...actually, the previous owner had the problem, did some hack to bypass it, and I fixed it correctly. Pretty easy to diagnose with some basic electrical skills, if you're so inclined. In my case, it was a faulty park position switch, which was a <$1 part from an electronics supplier like DigiKey (and an exact fit at that). To my knowledge, that switch is not an OE replacement item, but the solenoid and brake switch likely are.