That's how it works - each part is saved as a new model, regardless of how many times its used.
How it goes into Inventor will depend on how Inventor deals with Parasolids.
I would give a STEP and Parasolid, that way you should be covered.
bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.
Where would we be without sat-nav?