Here is the official expansion pack for Armed Assault, in otherwords you need the full game, before you can use this expansion pack 
As stated above this is the official release, however the team who packed this for you have cracked the copy protection on the same day it was released
I dont have this expansion pack installed as I dont have the original game, so I cant comment too much on it, but for those of you who do have the game and want this, I recommend on getting this
Features:
* New environments to explore and stage intense battles.
* Campaign consists of 7 missions, with multiple endings.
* Multiplayer modes allowing 6 to complete on a team.
* New weaponry including an array of US issue rifles.
* New vehicles including superbikes and DC2 planes.
* New characters including 6 completely new ‘dog solider’ characters.
* New features including equipment management.
* Arms dealers selling their deadly toys to you and your friends.
This expansion pack brings to the ArmA world two new story-based campaigns, all new multiplayer missions, new weapons, vehicles and characters, along with a new resource management feature and gun dealers.It also brings dozens of multiplayer and technical improvements, which finally enables North American players fight on the same battlefields as the International community.
System Requirements:
- CPU: 2.5 GHz Intel / AMD processor
- RAM: 512 MB
- Video Card: nVidia Geforce 6600GT with 256 MB RAM, Pixel Shader 2.0 or ATI Radeon x800 with 256 MB RAM & Pixel Shader 2.0
- Free HD Space: 6 GB
- Software: Windows 2000 or Windows XP and DirectX 9.0c
- For Online Play: Internet connection
- Original version of ArmA installed.