OpenPop is a continuous developing game by the help of the OpenPop Team. However you don't have to be in the team to help but you will be invited as a main developer if you help in any way regularly. There are many ways you can help develop the game from core coding to new graphics. You may just want to submit ideas, features or bugs, this can be done by submitting the idea on the forums.
You can download the latest source code from the downloads page so that you can view and compile the code yourself. You can also view the online code documentation here which was generated with Doxygen. If you have any code changes then you can submit them to any of the main developers or post it on the forums.
The recommended tool for compiling the source code is Visual C++ 2008 Express Edition, a free compiler from Microsoft which can load the project files included with the source code.