Not a streight forward game to setup so though a guide to help others was in order.
Launch Steam as Admin, right click the shortcut and click "Run as Administrator"
1 ) Download both ARMA 2 and ARMA 2: Operation Arrowhead through Steam.
2 ) Run ARMA2 then ARMA2:OA once then right click ARMA:OA and launch "Combined operations" to setup all the files needed.
3 ) Download latest DayZ Mod files from http://www.dayzmod.com/downloads.php
4 ) Navigate to your Steam folderMake and make a folder named "@DayZ" in your Arma 2: Operation Arrowhead directory.
5 ) Inside "@DayZ" folder create another folder named "Addons".
It should look like this:
C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\@DayZ\Addons
6 ) Copy the *.rar files to the Addons folder, unpack all DayZ Mod files in the "Addons" folder.
7 ) Need to install the ARMA2 beta patch head over to - http://www.arma2.com/beta-patch.php, the latest patch will be at top highlited in green. Download, extract and run exe.
8 ) Need now to configure the launch options for the mod to work. Go to Steam and right click Arma 2: Operation Arrowhead, go to 'Properties', 'Set Launch Options'. paste following parameters:
-mod=@dayz -nosplash -world=Chernarus
9 ) Run Operation Arrowhead and select "Launch ARMA 2: Combined Operations" to play the game.
If everything is installed correctly you should see "@dayz" line under "ArmA 2" on the right side of the menuscreen, to make doubaly sure, check in "Expansions" should be a green next to @dayz.
In multiplayer use the filter "DayZ" to find the specific mod servers.
GOOD LUCK AND
KEEP YOUR BAKED BEANS SAFE!!!