You format after you partition. Go into disk management, right click the drive you are trying to partiton and you will see an option to initialize. Click on initialize and follow the prompts. If the drive is 2Tb or less, use MBR when asked, otherwise you will need to select GPT. This is assuming you are running Vista or 7.
To get to disk management, right click imy computer and select manage, then click on disk management in the left pane.