just copy the files, and also when you goto run the game change the shortcut (or click on) the file to the other exe (i can't remember the name, i thinks its grim.exe) instead of the usual long named file)
Also if it complains about registry stuff, or its not installed copy the stuff below to a txt file, and rename it to a .reg file. Take care not to name it like grim.reg.txt! then double click on it.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\LucasArts Entertainment Company LLC]
[HKEY_LOCAL_MACHINE\SOFTWARE\LucasArts Entertainment Company LLC\Grim Fandango]
[HKEY_LOCAL_MACHINE\SOFTWARE\LucasArts Entertainment Company LLC\Grim Fandango\v1.0]
"Executable"="d:\\games\\Grim\\GrimFandango.EXE"
"Install Path"="d:\\games\\Grim"
"Source Path"="E:"
"CD Path"="E:"
"Analyze Path"="E:\\INSTALL\\DXDIAG.exe"
"Source Dir"="E:\\"
"GrimDataDir"="E:\\GRIMDATA"
"InstallType"=dword:00000009
"Version"="1.0"
"ExperimentalDisplay"=hex:01,00,00,00
"Last3DDevice"=hex:e0,3d,e6,84,aa,46,cf,11,81,6f,00,00,c0,20,15,6e
"LastDisplayDevice"=hex:00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00
"GrimMannyState"="suit"
"Magic"=dword:00092774
"MovementMode"="Character"