I had a fear of flying before i even climbed onto my first C130. But the scene of the terrain below you as you get to the door is an absolute rush! I strongly recommend doing it with a complete open mind. I wish i could still do it, but i've been out of the army for 12 years. I do miss those 82nd Airborne days!
Airborne school is really not that challenging and jumping out of a plane is actually pretty easy. The planes in Airborne only fly around 1200 feet, which isn't that high from the ground. You'll think that you're looking down from some high rise building, not a plane.
Here is how you get over your fear:
Rangers conduct operations that are many times more dangerous then any airborne jump will every be. If you cannot get over your fear of jumping out of a plane, you may not be good for Ranger battalion. Just suck it up, jump out of the plane, and you'll get used to it in no time.