I have been banging my head on this for a while now and I just can't
seem to get it figured out.

I have written a few XLLs in my day and now I want to implement an
extension function in a COM Add-In. I downloaded the CommAddin
example from MSDN and I have played around with it, but I just can't
figure out how the heck to implement a custom function and register it
with Excel.

I would be very appreciative if someone could point me towards any
information on how to get started in doing this, or better yet a
SIMPLE example, or (dare I even hope) step by step tutorial.

Thank you very much.

WKM