INSTALL GUIDE:

First go to your main folder of CoD4
Normaly in C:\program files\activision\call of duty 4 - modern warfare\main
If you have 64 bit windows it will be in C:\program files (x86)\activision\call of duty 4 - modern warfare\main

Now you must rename a few files:

rename iw_00.iwd to localized_english_aa.iwd
rename iw_01.iwd to localized_english_aab.iwd
rename iw_02.iwd to localized_english_aac.iwd
rename iw_03.iwd to localized_english_aad.iwd
rename iw_04.iwd to localized_english_aae.iwd
rename iw_05.iwd to localized_english_aaf.iwd
rename iw_06.iwd to localized_english_aag.iwd

Now you have done this you must make a new zip folder with WinRaR.
Make a map inside the zip named images. Now rename the zip to localized_english_aw07.iwd
(make sure you change the .zip extension into .iwd)

Now copy the mod files into the images folder you just created inside localized_english_aw07.iwd

This will also work with other mod files.