How can I drive a NEMA 17 stepper with a raspberry pi
Current matters far more on the ratings of a motor.  The voltage rating they list on the website is a DC voltage applied direct.  

from wikipedia: https://en.wikipedia.org/wiki/Stepper_motor#Stepper_motor_ratings_and_specifications

"Stepper motors' nameplates typically give only the winding current and occasionally the voltage and winding resistance. The rated voltage will produce the rated winding current at DC: but this is mostly a meaningless rating, as all modern drivers are current limiting and the drive voltages greatly exceed the motor rated voltage."

Go through the current limiting instructions on pololu's website and stay below the 1.2A rating.  Note the voltage ratings for the controller (as you need a minimum voltage to drive the circuitry).  There's some research to be done for supply voltage w.r.t. performance of the motor, and heat generation, but if you're not working the motor near it's rated wattage, you might not have to worry about it.