Jim,
That addon looks like it will do the trick for me. I installed the SQL file successfully, added the new PHP files, and copied and replaced the modified files over as well( thinking I didn't have to many modifications to the original OSC installation that I couldn't go back and tweek), however it was all screwed up. The main index page ( store front) was fine, but as soon as an item was added to the cart, things started acting up... on the cart page there was no "check out" button, then if I clicked "check out" from the main header menu, the browser went blank.
I'm now deleting the files in the "catalog" folder on the local and server and replacing them with a backup made prior to this addon, in hopes to get back to my original state. Do I also need to do something with the SQL file run on the database? I think I may have made a mistake copying the file over ( location wise) on the first go, so I am going to try and redo that first. But will I need to undo the SQl file to get back to normal if this doesn't work?