This has been explained so many times on the forums. Anyways, heres the gist of it..
1: Download and install
WinRAR
2: Right click the 'file archive' you downloaded from GCW and select the extract to.. option. Extract to somewhere you will remember on your PC
3: Copy the contents that you extracted from the 'file archive' to your installed FIFA 2004 Directory (usually something like Program Files/EA Sports/FIFA 2004). You will know when you are doing this right, because you will be prompted that a file with the name fifa2004.exe already exsists, do you want to replace it? Select Yes.
4: Double click that CRACK11NOCD4DEV.EXE. Follow any instructions it tells you.
5: Play the Game!