In xl2k and below, there was an addin named autosave that allowed you to do just
what you described. In fact, if you still have that addin, you can use it with
xl2002 and xl2003 (not sure about xl2007).
xl2002 replaced autosave with autorecover. This new feature was to recover data
if the system crashed (or excel crashed). Excel would notice that extra file
and offer to open it the next time you opened excel. But it doesn't save the
original file every x minutes like 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.)
If you really want autosave...
Gord Dibben posted this:
Autosave.xla from Office 2000 or 97 will work with Excel 2002 or 2003.
If you have a previous copy, move it to your Office\Library.
To download the 97 version see here........
http://www.stat.jmu.edu/trep/Marchat/sp2001/Library.htm