xl2k and below came with an optional addin called AutoSave.xla. It could be set
to save every x minutes (user selectable). And it just saves the file at those
intervals.
xl2002+ comes with something called autorecovery. It's also optional, but if
the user turns it on, it saves a copy of that workbook in a special location
(also user selectable). If windows or excel crashes, then the next time excel
opens, it notices that there's a file in that location. Excel prompts the user
to see if he/she wants to recover that file that was saved when excel/windows
crashed.
This autorecovery feature isn't used for the same purpose as AutoSave.
You may be interested in an addin that Jan Karel Pieterse (works in any version)
called AutoSafe (note spelling).
It doesn't overwrite the existing workbook when it saves. It saves to a user
selectable folder. And when it's done, it either deletes these backups (or puts
them in the recycle bin). And the user can always restore the backups from the
recycle bin.
http://www.jkp-ads.com/Download.htm
(look for AutoSafe.zip, not autosafeVBE.zip, for your purposes.)
Do you have access to the distribution disks to the older version of excel? Or
even access to a pc still running the older version of excel?