Not enough RAM
Jez,
I'm not sure how you can compare the DXF/3DS relation to the amount of RAM,
but here are a few suggestions. First, DXFOUT selected entities to bring down
the DXF file size. Next, make sure that there are not more than 64k
faces/vertices in each layer, color, or object depending how you are importing
the DXF in 3DS. Last, if all else fails try to bring the DXF into 3DS and turn
the weld function off, do this at a later time. If all of these fail you
probably need more RAM for the operation.
-Mike