We recently went through an upgrade from Goldmine 5.7 to Microsoft CRM 3.0.
It was quite the process moving not only our systems and processes to the new system but also migrating the data from Goldmine to Microsoft CRM.
We were lucky enough to have someone working with us, Jonathan Gill, who pretty stinking smart. He decided to not only migrate the data, but he built a tool to do it, and has released it for other people to use to help migrate a Goldmine database to a Microsoft CRM 3.0 database.
You can read about the project and download the tool at SQL Tree. He has also written about the specific project to Migrate Goldmine to Microsoft CRM 3.0.
If you are planning to use the tool for commercial purposes he asks that you would purchase a commercial license, but the tool works either way.