[GregT]

You can change the line thickness in Autocad. Select the geometry you want to change (make sure all layers are on) -> bring up properties -> look for line thickness.

OR you can change the line type by using the "line selector" combo box on the main toolbar (not sure if there is a technical name for this); select all the geometry, then use this box to switch it.

You might try using a different drawing conversion standard, i've seen dfx work well if you have access to it.

I tend to move .dwg to 3D models, not the other way around, let me know if these suggestions don't work and I'll try to figure it out tomarrow.

Greg