This Excel “AUTOSAVE.XLA” plugin (orginally from the Microsoft Office 2000 installation media) can be used to get the Autosave option in Excel 2003.

autosave.zip 23954 bytes

CRC64: 061C972E1E77329F
SHA256: 0EF8BEF0CED94437A93D79AAE62C7AC7330D87FC06C52663C41C541CA994C8C8

Virustotal Report, here.