Converting .DLL to .SO
You might try re-compiling the source code to the dll to a shared object. This may help you get started, after ensuring the code is indeed portable.
Edit:
Here is yet another link that can help guide you through the process of creating a shared library using GCC and other parts of the GNU tool chain. This link will help you to discover pitfalls that other people had when undertaking a project similar to this.
There is only so much help that can be provided for such a specific task, especially with so many unknowns. If you elect to provide more information in your question, please leave a comment.
NB: I'm pulling these links right out of Google.