Replacing .exe File

[JoyBoy]

its going to be something along of the lines of
C:\Program Files\EA Games\Fifa 2003 (Not to sure about this, cant be bothered to reinstall the game to find out)

You need to copy that crack into that Fifa 2003 folder. As cdkiller said, you will be prompted that a file already exists with that fifa2003.exe filename, do you want to replace it? well of course you do.