Imp DLL with function names and params ?

When I import a DLL, like with implib or impdef in Borland C++, I can use that DLL, but let's say it's not my own DLL like a Windows DLL, so, I don't know the functions parameters and the parameters type.
How could I get the informations.
Wrong answers are:
-read the doc
-ask the authors
-make the functions yourself

let's resume:
I would be able from a simple DLL to get the functions
that are inside, the parameters of those functions and
the types of those parameters.

thanks in advance.

      John.