If you have a non-Steam version but want to play online with friends using Steam servers, you can use a .

Ensure each computer has a different account name set in the configuration. Host a game on one PC. On the others, go to the Extra Content menu (like Mercenaries) and use Quick Match to find the local server. 2. Network Stability and Connection Fixes

This method allows you to use Steam's interface while simulating a LAN-like connection. :

: Copy the contents of the "Steamworks Fix" or "NoDVD" folder (often found in community repacks) into your main game directory.