Based on the assumption that you can now do this on a single workbook, you need to create a new template that you will use in future.....
1. Open a blank workbook and without putting anything into any of the cells, go to File, Page Setup and set up the footer as before.
2. Click ok to get back to your workbook and then go to File, Save As and save this as a new template *.xlt Call it something fairly generic but yet meaningful - don't reference a specific date or function that it will be used for.
3. Close Excel and go to wherever you have saved the tempalte to. Double click on the template and it will open a blank workbook with the footer details already populated. You can then save this as you would normally save a spreadsheet i.e use the *.xls file type.
4. In order to have the footer included, you should always use this template as the starting point for a new spreadsheet.
That should do it for you.