Now your all set, let me know if you still are having trouble
- Copy your modern warfare 2 folder located in /steam/steamapps/common
- paste it whereever you want it
- download the Client version update from the latest Modern Warfare 2 version (1.1.195)
its located here: https://www.mpgh.net/forum/269-call-duty-mw2-private-servers/142729-alteriwnet-1-3-37-cod6-private-server-install-update-instructions.html
- Just extract everything in the folder you copied
- Run the "alterIWnet_configure.exe" To set your Username
- Start the game "iw4mp.exe"