ok

# Go to Start -> Run-> Type regedit -> Hit Enter.
# Go to HKEY_LOCAL_MACHINE -> Software-> Activision -> Call of Duty 4
# Double-click codkey
# Save the key in notepad
# Replace the key with: DL2J8PY44Q22GE4888D2

after that...

go into C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\players\profiles
and make a NEW FOLDER, and name it what you want your characters name to be.
put the mpdata file u downloaded in it, and start cod4 up join MY SERVER... then exit, and change your key back AFTER your done