Excel XP & Win XP

I have a file that someone else created. It has a text box that appears
only when a specific cell is active and disappears otherwise.

I looked in John Walkenbach's book and read where I can toggle the visible
property of a text box with some event and get this effect, but this file
has no code in it at all. Anywhere.

I know how to link a text box to a cell so that the text in that cell
appears in the text box. But that is not the case here. This specific cell
is blank.

How is this done? Thanks for your time. Otto