1. Open the archive file with 7-Zip
2. Select the 'Extract' button.
3. In the 'Copy To' line paste you ArmA2 root folder e.g:
C:\Program Files\Bohemia Interactive\ArmA 2
4. Click 'OK' to start extracting the contents. Once extracted you can close 7zip.
5. If you have not already, install CBA
for ARMA2:CO you just need to copy the @CBA folder to your ARMA2 directory e.g:
C:\Program Files\Bohemia Interactive\ArmA 2\@CBA
6. Run ArmA2: Combined Operations.
7. From the main menu select 'Expansions'.
8. Left click '@CBA' and press the 'Enable' button
9. Left Click '@I44CO' and press the 'Enable' button
10. Click 'OK'
11. A warning message will come up that the game needs to restart. Click 'OK'.
12. The game should now return to your desktop, and automatically restart the game with the mod loaded. You should notice the Invasion 1944 Loading screen if loaded correctly.