NO-CD files question

[Rogue5]

when would i need to replace the .exe file with these, i have installed hitman, and played a bit, then installed the nocd .exe for hitman, and it still asks for the dsc, do i need to do this before i have played the game for the first time? or is it something else?
thanks, i really want to play hitman w/out the cd, but have been unable to do so thus far and attempting to copy hitman doesn't sound very easy after reading some of the posts about it.