the datasheet you linked to above is for a plain old DC motor, not an r/c servo motor. R/C Servo motors look like this: http://www.epanorama.net/documents/motor/rcservos.html
The motor you have will need a separate power supply as well as a motor driver circuit:
- here's a motor driver from ITP, using an L293 H bridge, with Arduino code to boot: http://itp.nyu.edu/physcomp/Labs/DCMotorControl
- Here's something similar from HVWtech in Canada: http://www.hvwtech.com/products_view.asp?CatID=113&SubCatID=146&SubSubCatID=0&ProductID=30
- here's another controller from Parallax: http://www.parallax.com/detail.asp?product_id=29144
All of the above drivers give you the opportunity to change motor direction via software commands; if you only want it to run in one direction, you can just use a TIP41 or similar transistor or Mosfet...
The R/C stores also sell a "servo-style" moduel that is equivaluent to the ones above, but it's usually expensive.
You'll also need a separate power supply to run the motor: connect the ground of the 12V motor supply to the Arduino ground, and run the +!2 to the motor, whcih will be in series with the controller.
Or.. and perhaps this is simpler... you can just get an R/C servo motor!