Because the source code for the OHRRPGCE is available to you under the terms of the GNU GPL license (version 2 or later, whichever you wish to use), if you make your own version of the OHRRPGCE, you need to release it under the GPL too. How do you do this?
- Read the full text of the GPL License. I know that reading lawyer-talk is a pain, but it is important to understand the license, and compared to most legal documents, the GPL really isn't so very difficult. If you are having trouble understanding something, feel free to ask James about it.
- Include a copy of the text of the GPL license somewhere with your program, and add a note to any readme file or documentation that mentions that your program is released under the GPL
- In the same readme and/or documentation, include a link to where people can download the source code for your program.
Note that creating engine plugins (separate .dll/.so files) does not allow you to get around the GPL; they have to be licensed under the GPL too.
Distributing Copies of GAME.EXE
You are not required to release your RPG file under the GPL. Your game is just a data file. You should still make sure that players know they can have the source code to GAME.EXE.