dc42:
Exactly. You only need to use a driver IC if you are switching the mosfet at high frequency, so for your application just drive the gate from the Arduino. That is what I do. For switching low voltages at low speeds, you can even do away with the series resistor.
One might also need to use mosfet gate driver IC for high power mosfets that are switching higher current loads even at slower PWM rates. The larger mosfets have significant gate capacitance so high current drivers can help the mosfets charge and discharge the gate capacitance faster, thus keeping the switching transition time shorter, which helps with the heat/power dissapation of the mosfet. The pretty high output pin current ratings of an arduino output pin works pretty well with most mosfet switching applications, however when talking really large current switching loads using large mosfets or mosfets wired in parallel, the purpose designed gate driver IC are almost always recommended.
Lefty