@blowdart: What are you talking about? TLBImport is for COM, not P/Invoke, and it doesn't generate a LIB file.
Also, you don't need the LIB file to use a plain DLL with exports in C++, you can use LoadLibrary/GetProcAddress, which is what C# does behind the scenes. In either case you do need to know the function signatures.
That was my point, you can use pinvoke without one, but if you try to add something that isn't viewable via Add Reference you need the lib, or a PIA.