Newbie - Making Windows Add-in with Python?

Help please!
I'm trying to build an add-in module to work with a shrink-wrap
commercial application. The API documentation supplied  with the app
shows how to build an add-in with VB or C++/ATL, in the VB example it
requires you to choose "add-in" and select the application for the
add-in. from deciphering the later documentation (I'm not familiar
with VB6) it implies that this causes the DLL Vb6 produces to be
registered in relation to the app, so that when the app starts it
autoloads the DLL.

I've had a play with the WIN32 COM extensions in PYTHON but can't see
how to duplicate the above behaviour.

Any clues please?