I'm 100% sure you can get 3d cad files into inventor. I haven't used inventor since highschool though. My college doesn't have any licenses for it, even on the engineering accounts. Hopefully they've got the student version up on their site and they didn't take out the import/export features like they did with Maya.
What format do you have the minufig in? Are you using m.dts that you ran through shaper or one of the ones floating around in 3ds or obj formats?