If you just hook things up like I describe above (using an N-channel, logic-level FET driver) all you have to do is set the pin to "1" to turn the backlight ON, and set it to "0" to turn it off.

PWM is not required unless - as Melanie says, you want to control the brightness of the backlight. And I have never seen a backlight that takes less than 200 mA.
You will not be able to drive the backlight directly from a PIC pin.