We use software which runs under DOS from Artwork Conversion Software in CA,
408-426-6163 to do both GDSII to DXF and back. It has worked quite well for us
so far.
Many mask houses can likely do this conversion for you for a nominal charge.
Photoscience has done it for us in the past (408-748-7673).
Good luck.
Signed: Hal Jerman, Ph.D., EG&G IC Sensors phone: 408-955-1211
Director of Technology fax: 408-434-6687
1701 McCarthy Blvd, Milpitas, CA 95035