The Windstar ignition switch (which is the similar to the other Fords that I've looked at) are designed so that the whole lock mechanism can be removed from the steering column by pressing in a pin that is located inside a hole on the bottom of casting in which the lock mechanism is inserted.
The key is necessary do this, so you need to turn the key to the "Run" position to remove the lock mechanism, then press the pin while pulling the lock assembly from the vehicle.
Replacement cylinders with new keys are available from most autoparts stores, or you might find that a generous application of WD-40 or some other light weight oil will improve the movement of the key.