Autodesk has released a Rhino 3DM importer for Autodesk Inventor 2010 and Autodesk Inventor LT 2010. All versions of 3DM are supported.
This translator reads
Rhino files(*.3dm) bringing solids, surfaces, wires, and points into
Autodesk Inventor to be directly utilized while modeling. Being able to
import directly from Rhino files eliminates the need to convert the
Rhino data to make it usable in your projects.