I've had the same problem with my 03...and usually it's because the wheels were turned when I shut off the engine and held the steering wheel straight. It puts too much pressure on the 'wheel lock' to allow the key to turn.
Best you can do is turn the wheel back and forth as much as you can while trying to turn the key. Don't force it-you'll break off the key. When it hits a spot with less 'pressure' the key will turn easily.