Hello,
First be clear, Servo-motors have only 180° turning possibility, so you would say more acurately "positioning" than "turning".
Yes you can send a servo to different positions, using "servo" or "servotimer1" library and using the value of your photoresistance to the servo angle.
If you want to turn something and change the speed and direction, you must use a DC motor with a L293 chip, a PWM out for speed and 2 binary out for direction. Search in the wiring site (http://wiring.co.org) to find design.
You will find sample in the Arduino playground.
jhoepffner