The latest version 2.5 of OscMax comes with the one page checkout installed. I want ONLY the one page checkout be installed for my older version 2.0.25 of OscMax. You need to install both versions in your local server and test to figure out what files or codes need to be copied to the older version, and also the script to add any needed info to the database, so I can follow the same procedure to add the OPC. Another approach for this is via the OPC addon for Oscommerce if you think it is easier to convert the STS to BTS. Similarly, I need the procedure, so I can install mine in my local server. In fact the OPC of OscMax 2.5 is based on the Oscommerce addon. Here is the info for the addon.