Unfortunately, it appears that direct export to 3DS format was removed in AutoCAD 2007, which means this program is not suitable for dwg to 3ds conversion anymore. Autodesk suggests that users export their DWG files to FBX format, which can then be used in all sorts of 3D modeling / CAD tools, including 3ds Max.
Some 3rd party solutions might also allow users to convert dwg to 3ds, albeit only with certain versions of DWG and 3DS files.
Open DWG file Open 3DS fileAn online CAD conversion service
A commercial online CAD converter
A 3D CAD translation software