Why not try this advice ?

<< there are plenty of inexpensive standalone DWG to DXF and vice versa converters out there.rt

And take a look at this free thing! ;)
Maybe you can import any 3D format then export in any 3D format! ;)
http://www.simlab-soft.com/3d-products/simlab-composer-lite.aspx
(just carreful : the 3dm from Moi is not supported so use stp/Step, iges/IGS or Sat )