Hello,
I would like to do some interprocess communication between an
MFC regular DLL and Microsoft Excel, and I am currently using a
VB6 app as an interface to execute various Macros. I would like to
know if a COM Add-in could do something identical or similar. I
dont know what a COM Add-in does. I have created numerous
COM objects in J++6 and added them to UserForms in Excel,
but this is not the same as a COM Add-in is it ? Where can I get
some info on COM Add-ins?

If you do a search on MSDN you should find several articles.

http://msdn.microsoft.com/default.aspx

--
Jim Rech
Excel MVP