+12V | .-. | | | | Fan '-' | Pin 11 - PWM | |/ o-------| |> | | | | === GND
Let's go back to the beginning. Why do you want to control the speed of the fan using PWM? What is the fan doing that requires varying the speed?
its like the wind blows in his face as he goes faster!!
If the fan isn't designed for PWM control, you can always make a simple low pass filter to turn the PWM into a pseudo analoge output.