You have to have Steam and a Source game to play GES online or over LAN, no if's, and's or but's. However, you can log into Steam on one account online with the Source game installed, then disconnect that computer from the internet but have it remaining on the LAN, then log in another computer to same computer and do the same thing, and so on. I think you can play LAN that way, but it will boot everyone off of the account except for the last person to log in after reconnecting to the internet.