DLL and LIB are not needed.
All you need to do is create a makefile and compile it using MingW 3.1 (not 5.0)
Easiest way to do so - at least out of my sight - is the usage of Dev-C++ where you add a second compiler which is using 3.1 MingW installation you did for BM instead of the default (which is MingW 4 or 5 which is incompatible to BM)
After that, you create a new project (for static library), add all the source and compile it. With a little luck you already have some kind of project file (.dev is Dev-C++) you can load or at least import and either use directly or just have to change to compile to static library in the project settings.
All you need to do is create a makefile and compile it using MingW 3.1 (not 5.0)
Easiest way to do so - at least out of my sight - is the usage of Dev-C++ where you add a second compiler which is using 3.1 MingW installation you did for BM instead of the default (which is MingW 4 or 5 which is incompatible to BM)
After that, you create a new project (for static library), add all the source and compile it. With a little luck you already have some kind of project file (.dev is Dev-C++) you can load or at least import and either use directly or just have to change to compile to static library in the project settings.