Hi flim, for sketch data like lines, arcs, polylines, etc.. try using DXF format for those. In MoI v4 the DXF import can also read layers now.

DWG is unfortunately difficult to support, it is not documented by AutoDesk and so it needs special libraries to be licensed in order to use it. DXF is documented (for drafting type entities, not for 3D solids though) and can contain everything that a DWG does. Usually if a program supports DWG export it also supports DXF export as well.

- Michael