Simply extract the .rar and put the .iwd in your MW2\main folder.
If that doesn't work or just you don't know how to do it correctly:
Open your iw_07.iwd file in your MW2 game repository with any .zip archiver. And go in the images folder. Simply drag and drop the content of the mod "iw_07.iwd folder" in the iw_07.iwd.
It will ask you if you want to replace the files,Click yes and your done !
Don't forget to backup the original Iw_07.iwd or just the non-modified files if you want to remove this camo