controlling a fan's speed (low power usb desk fan)

Hi guys & girls,

Recently got my Arduino, exciting!

I'd like to make a project that controls speed of a fan on a users desk, from say 0 (off) to 100 (full power). The easiest way I can think of is varying the amount of electrical input to the fans motor.

I will sync this up with some kind of experience on the screen, where perceived "wind" blown at the user is variable.

Not really sure where to start. I can program the variable for wind speed easily enough, it's more the electronics side I'm new to.

Before I fry the board or electrocute myself, does anyone have advice for getting such a project started? (or even know of a similar project spec I can err, borrow?)

Thanks,

(pc fan is fine if that is easier / cheaper - if the variable effect can be felt by the user)