Ken,
The inheritance item that you are looking for is a feature, not a part. It is under the Insert/Shared Data/Inheritance or Feature/Create/Shared Data . The inheritance feature allows you to open a second part for import into the one you are working on. The cool thing about this feature is that it brings along the features instead of just a lumped copy (like an iges file or Copy Geometry feature). That way you can delete/reorder/or modify the features without the pain of dealing with surface operations.
-Wayne