I'm currently in the process of transitioning from AutoCAD to Inventor.
How do I export my 3D AutoCAD models directly into Inventor as parts?
(which I can later use for assembly)

Hoi, You open an new Inventor part.Close the sketch.Import the dwg you want.You will see that a window where you can addapt al the parameters you want. 

i have the some problem with importing cad library from http://cad-download.cadincadout.com/ 

someone can help me with it?

Hoi Basia, i assume this is your name,can you explane wath is going wrong.It is not possible to help if the problem is unknown. regards, Danny 

You can use the tip:http://www.cadforum.cz/cadforum_en/import-autocad-3d-dwg-files-into-inventor-tip8528