Next time don't forget to make backups of the files you are going to manipulate before you do!
If you have an extra PC that does not have Arma 2 OA installed, you could-....
Ho! Stop, No.
Why would you want to make a backup of your files in such a wonky, silly way? You don't need a second computer at all. All you gotta do is make a copy of your pbo's and dump them in a recognizable folder (i.e "OA_BackupOriginal" or "OA_BackupCheats" and place them somewhere easy to remember.
Save yourself the embarrassment by not backing pbo files up on a completely different system, if you must, just put them on a portable harddrive.