Hi Hamish, you're probably going to need to contact Alibre support to find out if they can import curves and from which formats that is supported.

MoI will write out 3D curve information to 3DM, IGES, STEP, and SAT formats (STEP and SAT are added in MoI version 2).

But doing a quick test, it does not seem that Alibre may only be looking for surface/solid information in these formats and possibly skipping individual curve objects that are in the file.

One other thing you can try is to save the curves to 3DM format, and run the 3DM to DXF converter for curves which you can get here:
http://moi3d.com/wiki/Resources#3dmCurves2DXF_converter

I tried with some planar curves and the DXF file that comes out of that converter seems to go into Alibre, but into the 2D sheet editor instead of into the part editor though.

If you find out from Alibre support that there is a way to export 3D curves from AutoCAD into Alibre, you could get things through that way by bringing the curves into AutoCAD by DXF format with the converter above.

- Michael