Standard pinout, same as high end 4 wire GFX card fans:
1 2 3 4
GND +12v Monitor PWM
(BLACK) (RED) (YELLOW) (BLUE)
GND = Ground
+12V = 12v from PSU
Monitor = pulses once every rotation of the blades.
PWM = lowering the voltage at this pin (the fan has an internal circuit that puts power on this pin) reduces it's speed.
And here: http://thereifixedit.failblog.org/2012/03/05/white-trash-repairs-milkforce-gts/
Notice that I used an XBOX360s fan on that repair and I didn't change anything on it, that was Plug and Play.
edit: And a hint from me: Cutting the blue wire makes the fan run AWAYS on maximum speed.