(64bit system) After installing, extract the folder then open the SETUP.exe . There you go!
(if the thing above fails, use the instructions below)
(32bit system) after installing, OPEN the folder. Inside there will be a SETUP.exe . Re-name the SETUP.exe to SETUP.zip and click "yes" when it asks you if you want to change it. After it changes, Extract it to anywhere on your PC you would like.
Then you are ready to go! the GL2 is the recommended version of the game to use.