Ok,
I have a transistor.
Is it npn or pnp, or better yet what is it? TIP120, or what?
If you hook the motor across the 9 volt battery, does it spin as you would expect?
Do you also have a diode we can place across the motor to help protect the transistor?
We are just about there.
Once we get all these parts in place, what do you want the arduino to do first, Turn the motor on and off ever second. (Just first test?). Sounds good. Use the blink example program (have you got that working yet?), then we can change the output pin to control the transistor. (I am hoping that is an NPN transistor). Let us know .
It's getting sorta late here. If you don't hear back, that means I have turned in for the night, and will be back on tomorrow.