For general C/Nimrod interop see these Rosetta Code tasks:

http://rosettacode.org/wiki/Call_a_foreign-language_function...

http://rosettacode.org/wiki/Call_a_function_in_a_shared_libr...

http://rosettacode.org/wiki/Use_another_language_to_call_a_f...

Making c2nim work with header files can be a bit difficult. The main information is here: http://nimrod-lang.org/c2nim.html

When something throws an error I comment it out and try to see if I can fix it up by hand.