I had my 2000 S-Type dash wood restored by Madera Concepts, but with a much darker stain.
Now of course, it does not match the steering wheel.

The only dark wood Steering Wheels i've seen on e-bay are 2003+

I've noticed the S-Types > 2003 differ a bit in construction.

Will a 2003+ Steering Wheel fit and function in a 2000?

EDIT:
I know that if it would fit, that the airbag and switches would have to be from the same year(s) as the wheel.

 

I don't think so.
The 2000-2002 wheels have an inverted U-shaped piece in them, and notch on the side.
The > 2002 wheels have a U shaped piece, and notch at 6:00.