brushless motor

how can I control a brushless motor?

Driving stepper motors - unipolar or bipolar:
http://www.tigoe.net/pcomp/code/category/arduinowiring/51
Driving hard drive motor:

(the latter does not provide code, but provides clues and coil energizing timing, so you can adapt code and circuity from the first link to drive a hard drive/cd rom drive brushless motor)

Depending what sort of control you need, a radio-control type brushless DC motor speed controller might work. You'd have to drive it as if it was a servo.