One additional question: Is this code I can add to the add-in (the .xla
file)? Or am I going to need to add it to an Excel file?

If I"m understanding Chip Pearson's sample file correctly, if I want to
trigger an action that occurs every time a workbook is opened, I'll need to
have some .xls file containing my code open, too.

And so my solution seems two-fold:
1. Write code that triggers an action whenever a workbook is opened.
2. Write code that opens the doc containing the code for #1 any time Excel
starts.

Just want to make sure I'm heading down the right path.

Thanks.