This file might be a help:
http://www.bygsoftware.com/examples/zipfiles/doublesave.zip
It's in the "Administration Utilities" section on page:
http://www.bygsoftware.com/examples/examples.htm
This saves a workbook and creates a backup version in the same directory.
Click on the button and the workbook will be saved, and backed up, into the
directory where you downloaded it.
There are two backups created with this version: one as
filename_yyyymmdd_hhmmss.zip and filename_yyyymmdd.zip. The first gives you
an incremental backup everytime you save your work. This is especially
useful when developing workbooks. The second ensures you have a daily backup
based on the final save you make each day.
The code is open and commented.
Also, take a look here for Byg Software's Save and Backup utility:
http://www.bygsoftware.com/saveandbackup.htm