I have downloaded the files and the zip contains a DLL, some simple readme file and some C++ example files.

1 >>I suggest you download dependancy walker.
This will give you more info about the exported functions and the DLL dependancies.

2 >> Check out the C++ files and try to translate them to pascal.
Most likely, These will contain a lot of info on how to use the LIB.
I quickly looked at BB_DInput.cpp and i think it can be translated to pascal.

Ask more specific questions when you get stuck while translating.
(Translating code is not my specialty, so i dont think i can help you with that, but i'm sure others will )

Good luck