Well, I found the answer:
"try this... go into C: drive, look for the Activision folder, open that, you will see a folder that says players, open that you will see a folder that says profiles copy and paste that folder to a backup hard drive, flash jump drive, cd or what ever you choose.
this way if you ever loose your stats, harddrive, what ever , you can just reinstall the game using your original screen name, log on to multiplayer then logout close out the game, replace the "profiles" folder into the C: Activision\ players\profiles and paste your saved b-up over the new one choosing yes to all when prompted, you will have all your controlls, stats, etc back. you need the new patch as well I believe its 1.5.
Or:
This seems to be a great little tool to back your rank up, that way you won't have to worry about the IW server crashing, not saving your rank, and you being shiz out of luck.
Heres the download.
Size: 403kb
Name:
CallofDuty4Backup0.9.2_Sep.exe
"