Sounds like fun. Is this all I'd need to buy to be able to play? http://store.steampowered.com/app/33930/
Steam-version installation:
1. Download both ARMA 2 and ARMA 2: Operation Arrowhead through Steam (Combined Operations)
2. Open both of the games to allow them to install the required files, then close them
3. Download all of the DayZ Mod files into a folder
4. Make a folder named "@DayZ" in C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead (or your Operation Arrowhead base folder)
5. Then make a folder inside "@DayZ" named "Addons"
6. Paste all of the downloaded files inside the "Addons" folder
7. Extract all of the downloaded files
8. Go to Steam and right click, properties, set launch options on ARMA 2: Operation Arrowhead
9. Insert "-mod=@dayz -nosplash" and click OK
10. Open Operation Arrowhead and select to "Launch ARMA 2: Combined Operations"
Game is a bit expensive on Steam, especially if you're just buying it for a mod in Alpha but it's completely worth it. It's the most tense game I've ever played, because you can die at any time and lose everything, either by zombies or other players (Bandits).