Hoever you can (by direct register manipulation) reprogram the PWM rate from the default (which about 500Hz on some pins, about 1kHz on others). This requires understanding of the counter modes and registers. You probably want a PWM frequency of 50 - 100Hz or so to get sensible behaviour from a servo.
Of course the Servo library is an even better idea as it can drive more pins and isn't limited to the PWM-capable pins.