I am considering using DDE for this because I am having a very hard time
figuring out how to connect to Excel from a C++ app (using automation)
and then register or somehow get notified of changes to a particular
cell on a worksheet.

No need to provide me the code - just a pointer to appropriate
documentation. I have found some things that appeared to be promising,
but nothing I see allows me to do this.

Any suggestions are welcome.

thanks
tim