Did you check the little box that says "Show all variations" or something like that on the airplane choices screen (sorry I'm not at a computer that has FSX right now)?. If you don't, it will show just one of each kind of aircraft, not all the available textures.
If that is not the issue, you can check two other things:
1 - is there a WW texture folder in the particular airplane's folder in "Simobjects"?
2- does the 'aircraft.cfg' file have an entry [Fltsim.xx] pointing to that Westwind texture?
If so, and you're still not seeing it then I am at a loss!
Good luck, write back to let us know if/when you solve the problem...
Matt Smith - WWA2218
Washington DC (KIAD) Hub