Hello again 
A few questions regarding computer fans (PWM) and controlling them with arduino.
The one I'm will be using has a 4-pin connector, The pin layout:
I'm guessing:
Blue- PWM signal
Yellow- RPM sensor
Red- +12V
Black- Ground
So I'm thinking: hook the fan up to 12v and send PWM singals from arduino via the blue wire, would it work?