You will need a file called a "crack". This file basically tricks your PC into believing that the CD has been placed in the drive. Naturally, this is what people who dont legally own games use most of the time, so the legality is up to debate.See http://en.wikipedia.org/wiki/Software_crackingHowever, cracks for games that you own (wink, wink) can be downloaded from gamecopyworld.com.See http://m0001.gamecopyworld.com/games/pc_rollercoaster_tycoon.shtmlOnce you download the crack, replace the .exe file on your PC with the crack, and the game should never ask you for a cd.Or you could make an image of the CD (if you have it) and mount that image whenever you want to play.