If you bought the game at GOG then install innoextract and download the Windows installer.
Roller Coaster Tycoon 2
The RollerCoaster Tycoon 2: Triple Thrill Pack is mandatory. Extract it's contents with
The game contents are in the app folder. Move it to a place of your liking. The game will ask you for this location at first startup.
Roller Coaster Tycoon
RollerCoaster Tycoon: Deluxe is optional.
To extract it run
Again move it to a place of your liking. Go to the in-game settings and choose the folder where you placed it. After a restart the original campaign will be available to you.