I am trying to search for a drivers door module for a 2000 Century, and I am not getting any clean hits, so I am a bit leery. I can't even find a DDM for a 97-05 Park Avenue, which was designed in the same era, which also worries me.
I am concerned with the whole idea however, unless you are buying the Century for parts for another car, or for parts profit. The engine is different (3.1), the chassis is different (W-Body), and the brand is different (Buick), so there are 3 things working against you right there. Also it seems like GM carried a bit different of a mindset when they designed the new chassis for the '97 model year (C and W bodies) and the '00 model year (H bodies).
I think the list of shared parts will be relatively short, and don't think buying a parts car for a blower motor that you don't need is the best of ideas.