Here's a quick, sneaky way to do it.

In the other workbook, create a short, dumb macro like "Range("A1").select"

Now, when you want to open it, in the current book just say "Run other
book's dumb macro" (you can record a macro to do this).

If the other book is open, the dumb macro will run and that's it. If it's
not, the "Run" command will open the book and then run the macro.


HTH
Paul