90% of the worlds desktop PC's have 12v fans running at much lower voltages, usually using variable resistance controllers. Even the 5v supply we are talking about could be a PWN running at a startup of 3v.
I can't say if this is true or not but I do know that all pertinent information is important to include in our threads. I'm sure you'd agree.
If your port is 5V PWM it can be used with a 12V wallwart and a transistor switch. It will essentially produce a 12V PWM signal to the motor.
Chris