So as a topic states down below Arma Combined operations is 15 bucks on amazon! so i jumped on that seeing as how im dying to try Day-Z. but to my dismay i found out (after the fact) the Arma cd keys are not redeemable on Steam. so i'd have to download it from Amazon... for 7 gigs its going to take over 42 hours! which sucks...  

Combined Ops is 7 and 8 gigs for ~14/15gb total for everything you need to play Day Z. Yeah, it does suck, but honestly it took me just as long to download and install it all from steam as it took my girlfriend to DL and install from amazon.

Here's some instructions specific to the Amazon version to get it working:

I've been hearing that a lot of people are having trouble getting DayZ to work with an Amazon-bought copy, so here's my guide. I've installed two different copies now with zero hiccups, so hopefully this works well.

Also, like Rocket said, it's probably a lot easier to just buy the game through Steam, but if you're like me and weren't aware that Amazon was ripping off the devs and bought the game anyway, this should help.

Anyway, when you buy ArmA 2: Combined Operations, that's just an overarching name for the pack that includes both ArmA 2 and ArmA 2: Operation Arrowhead. Combined Operations is not a game. It's just the name of the pack.

Installing and Patching ArmA 2

1) Install ArmA 2

2) Install ArmA 2: Operation Arrowhead

3) Download [1] Patch 1.60 and install it. It will patch both games (ArmA 2 and Operation Arrowhead) so no need to worry about separate patches for each game or anything.

Installing the latest version of DayZ

4) Download [2] worrom's DayZ Updater and extract the contents of the .rar to somewhere safe.

5) Go into the contents of the DayZ Updater folder, find the folder labeled "config", and the file named Settings.properties.

6) Open this file using Notepad or TextEdit or whatever, and find the line labeled "GameDir = C:\\Program Files (x86)\\etc etc blah blah"

7) Change this line to wherever you installed ArmA 2. By default it should be "C:\\Program Files\\Bohemia Interactive\\ArmA 2\\" unless you changed it yourself. Don't forget those two slashes at the end.

8) Hit save and exit Notepad. Now you can launch the DayZ updater and hit "Check for Update" or "Force Update". The only difference is that forcing the update redownloads and replaces all of the update files, just in case something went wrong last time you updated.

Making a shortcut to run DayZ

9) Go to your ArmA 2 directory, find the file labelled "arma2oa.exe" and make a shortcut to wherever you want to run the game from. This shortcut will be what you use to launch DayZ.

10) Right click on the shortcut, hit Properties, and at the very end of the line that says target, add the tags -mod=@dayz -nosplash

And that's it, you're done.

You can now safely and quickly run DayZ at any time by just using that shortcut that you made. You can update DayZ at any time by just running worrom's DayZ Updater and hitting Check for Update.

EDIT: I also hear Six-Updater is a good way to install and update the DayZ files. I haven't tried it, so I can't really say much on the topic. If you do use Six-Updater though, it would be replacing steps 4-8 of this process. worrom's seems to be working fine for me, and the way it's designed is pretty future-proof as long as the link hosting the latest DayZ files doesn't change.

(Courtesy of reddit user Spleendor - http://www.reddit.com/r/dayz/comments/tx1wn/installation_guide_for_those_of_you_who_bought/ )

I would also personally recommend the latest Arma2 beta patch to play on beta servers (local voice chat actually works most of the time, which is a very useful, important and fun part of the experience. Here's instructions for that:

First things first, go to the ArmA II Beta Patch website and grab the latest version listed at the top. Once downloaded and ran, it will install like a mod, into its own addon folder. Go to your operation arrowhead install directory, then locate and edit "_runA2CO_beta.cmd" in notepad. Near the bottom you will see a few lines pointing to the beta executable and two -mod strings. Add ";@DayZ" to the end of the first, then save the file, and run it. Create a desktop shortcut to it if you'd like.

(Courtesy of Something Awful forums user rizuhbull - http://forums.somethingawful.com/showthread.php?threadid=3481582)

Happy hunting, and remember - don't kill anyone named Gray in cold blood for their beans. That's me. :)

H@Nerolus: Hey thanks for the info. After the download finished for Arma II i got half way through installation only to be greeted with a big fat CORRUPTION ERROR! needless to say. i really didn't feel like downloading the fucking thing again, and started playing Diablo. im sure i will get back to it at some point, and i'll be sure to keep your info in mind!

Edit. never mind, never mind. i dont care if i wasted 15 bucks on the Amazon version. im buying the steam version...