I have a friend who bought MW3 via Steam. He can play original and 4D1 in same time ? In past Steam directory contain an folder with Steam ID, and in that folder were installed games.

he cant if there is the same directory, however if he has a alternative FD1 installation Directory then yes he can.

I know,my friend need to have 2 games directory (original and 4D1).Question is: he can install Steam in two location, because both version need Steam.

 

Later edit: i have two possible solution

 

1. If 4D1 need Steam only for first download (for fresh files),my friend can run game from another location without 2 Steam installed

2. If 4D1 need steam my friend can add 4D1 in Steam on section Non Steam games

Your friend doesn't need to install Steam twice. Having Steam running when you launch the game is enough.

Just copy the game folder to somewhere, apply 4D1 patch on it and then launch the game with Steam application running.

well no you dont need to copy the files anywhere cause' the 4d1 executable files are LaunchIW5M.exe and not iw5mp.exe so yes you can run both of them at the same time

even the dedicated server files are different..... so there should be no problem

well no you dont need to copy the files anywhere cause' the 4d1 executable files are LaunchIW5M.exe and not iw5mp.exe so yes you can run both of them at the same time

even the dedicated server files are different..... so there should be no problem

That.