You can try and use CFF Explorer as well. Install it, right click on the main game executable, open with CFF Explorer, on File Header you will see Characteristics, and to the far right at the end of it you will see a bluish part saying Click Here, it will open a a tiny box with Check Box options.
In the box you just need to Check the box that says: App can handle >2gb address space. Then you will need to leave, it will ask you to save, you save with the exact same name as the executable and just start up the game.
This is basicly the 4GB Enabler if you want to do by yourself.