Display a Message box while opening a XLS file
 

Hi,
I have this folllowing situation for which I need your help - I have office XP and a XLS file with many sheets. All I want is that whenever this file (any sheet) is opened for the first time in a NEW MONTH then a custom made message is displayed with OK and CANCEL buttons. I CANCEL is pressed then that message box would not appear for that month at all.

But if OK is pressed then that message should pop up whenever that file is opened again in that month or the users navigate across sheets. I know this could be annoying but that's what the users want. This should go on until CANCEL is pressed. NEXT MONTH the same procedure should follow.

Pls. help me create this program/macro.
Thanx