VicK: Yes, to a small degree.
It takes power (several HP) to drive the AC pump. This power is taken from the motor by the AC drive belt, so it loads up the motor slightly more, and it uses a little more gas.
It's not a huge amount, and it's certainly not worth getting heat stroke over.
It can but temporarily.
The air conditioner takes less energy than wind drag of having your windows open.
Yes, but not enough to make much of a difference. The way you drive has a much more significant affect, as does having proper tire pressure.
If you mean air conditioning, the answer is generally yes: Air conditioning usually requires more fuel consumption, but the percentage of degradation will vary by the car, engine, speed, driving habits, design of the a/c system, etc.