Ok, so with 90% of other steam games if i reinstall or need to copy a game folder across to my gf's pc i do just that copy it across and its good to go.
Now i had massive issues trying to use the game files that i had from like 7-8 months ago for reinstalling arma 2 and OA, so i had to download both.
I then copied both the folders onto my gf's pc and started up steam, OA showed up in the game list as white and just went ahead and did the battle eye and directx installs and worked perfectly.
ARMA 2 on the other hand...... it doesn't matter what i do, tried copying all the files into the common folder where they are after they have been installed and it just starts downloading the 8GB. So i tried transfering the files into the downloading folder to see if it would pick it up there and speed through the download and nope still wanted to download all 8 gb.
Is there anyway to get arma 2 to copy across and not have to download the whole game? Seems ridiculous that OA can do it but arma 2 has nothing but problems.