DayZ Mod ! Only Arma II ?

You need OA.

Nope, you need Operation Arrowhead

The DayZ Mod requires both Arma II and Arma II: Operation Arrowhead.
Please read the product page on Steam: DayZ Mod.

At one point I knew there was a free version of Arma 2 knocking about with reduced textures etc. You could combine it with Operation Arrowhead (you had to buy that) and play the mod. I was curious, is that still the case?

I never did it, got the paid versions of both and am just wondering. OP's question in reverse!

I think that you want to get Humble Weekly for $1 to get ARMA 2 to unlock DayZ mod. But unfortunately, DayZ mod requires both ARMA 2 and ARMA: Operation Arrowhead to play according to steam store page. So, only having ARMA 2 is NOT enough to play DayZ mod.

Operation Arrowhead (standalone game from arma2) is Mandatory. However you can play Dayz using arma2free (available on their website) along with OA. Doing this will prevent you from using high resolution textures. If you are on a cheap rig without much video RAM I would suggest you to do this as you'll probably be playing with low-res textures. Hope this helps!
You can get OA on the cheap here: http://www.gamersgate.com/DD-ARMA2OA/arma-2-operation-arrowhead

Maalesef,DayZ için Operation Arrowhead olması gerekiyor.Bazıları onsuz da çalıştırmak için modlar kullanıyor ama oyun düşük çözünürlükte oluyor ve sürekli hata veriyor.Ama zaten $6'ın her kuruşuna değer bence, Arma II zaten çok iyi bir oyun bir sürü de modla çok daha zevkli oluyor.DayZ sadece modlardan biri.