An oscommerce ecommerce store uses an addon linked here: [url removed, login to view]
The add-on creates a PHP page which pull up orders from the ecommerce store using different filters of your choice.
You would have to create a button on this page that would export the information that the code produces into an Excel file with the template provided.
Basically, you would have to change [url removed, login to view] into a usable Excel file as seen in [url removed, login to view]
Please be perfectly confident you can achieve this. Showing me a perfect example would earn you the job immediately.