Before Printing Workbooks: Prompt For Footer/Header

Before printing ANY workbook, I want the user to have the option of adding a footer.

To start out with, here is the code I have:

Sub Workbook_BeforePrint(Cancel As Boolean)
'When you click 'Print', this module asks if you want to add a footer.
'The one it adds by default is: Path & filename, worksheet name, date.
'Unfortunately custom button text is not available, so Yes means add to
'current sheet, No means no, and Cancel means add to all sheets in workbook.

Dim answer$
Dim sheet As Worksheet

If ActiveSheet.PageSetup.LeftFooter = "" Then 'if there isn't a footer already
answer = MsgBox("Do you want to add a footer?" & vbCrLf & "Yes - this sheet only, Cancel - all sheets", vbYesNoCancel)

This works just fine if I put it in the ThisWorkbook section of a workbook. The problem is I can't get to work for any old workbook. If I put it in personal.xls, nothing happens when the user clicks print.