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