This following package is based on the Discount Code for osCommerce 2.3.1 Addon.
I was able to reduce the install process from 16 steps down to 9 steps.
Database tables and filenames definition have been removed. I tried to keep the code changes to a minimum.
SQL install/uninstall is done automatically with the ot_ module.
It should, but I don't remember having it tried. Just try, installation is easy and fast.