Play pc game without disc?

im trying to play rollercoaster tycoon 3 without having to use the disc. Ive been looking it up and i went to www.gamecopyworld.com and downloaded the rct3 file there and the used power archiver to extract it into the program file and overwrited the original exe. But when i try to play the game it takes me to the main menu and when i try to start a game it begins to load then stops and says something about not being able to find the female heads??? i dont know what to do