Your tranny shouldn't be leaking. Is it coming out of the pan or the seals? If so, then you have a problem. Are the pan bolts tight etc? Regardless of the above, you should be able to fire up the engine without causing any harm to the transmission. After you fire it up, let the engine warm up and then check the transmission level. If it's okay, then with your foot on the brake, slowly run the transmission through the gears and see if the transmission goes into gear. Let the transmission stay in each gear for 10 or 15 seconds. Then check the transmission level again to see how it is. Shut off the car and wipe off all the transmission fluid that has leaked everywhere. Restart the car and check the fluid level and check for leaks by running the transmissin through the gears again.