If you are a Windows user, the self-contained EXE version of the game will be the most convenient option for you. Download the ZIP file, extract it, and run the EXE file within it.
If you do want to run the source release, you must install the Python 2.4 and Pygame 1.7 libraries.
To install Python, visit http://www.python.org/download/ and select the latest version of the Windows installer. Download the installer, open it, and follow the on-screen instructions.
To install Pygame, visit http://www.pygame.org/download.shtml and choose the Windows release. As before, download it, open it, and follow the on-screen instructions.
Once Python and Pygame are installed, the game is ready to run. Click on the LightYears icon to start the game.
Then, ensure that Python 2.4 and Pygame 1.7 are installed. Most modern distributions provide versions of Python and Pygame: use the standard installation method for your Linux distribution.
Finally, start the game by typing one of the following commands within the game directory.
./LightYears.py python ./LightYears.py python2.4 ./LightYears.py