Using the mosfet as shjown in that diagram, you should connect a 100 or 220 ohm resistor between the Arduino output pin and the mosfet gate. If you substitute a TIP120 for the mosfet then you MUST connect a resistor between the output pin and the TIP120 base terminal. 1K will do. The disadvantage of using a TIP120 is that it has a voltage drop of around 2 volts, which means it will get hot and need a heatsink unless the motor current is small.