I already posted here 10min ago, but the forums died for some odd reason. Stupid database error. Anyway, he is not using steam due he can play Half-Life fine, but can't play Earth Special Forces. Steam is required in order to play Earth Special Forces stabel and legally. Download Steam, install it. Then you have to create an account which you can do when you launch Steam. Just make sure you have a legal key to enable your Steam account in order to download Half-Life / Half-Life 2 / Counter-Strike, etc (depending on which package you have bought). Once you have done that, check this thread for all the help you need:
If it tells you the key you are trying to put in Steam is already in use. Buy Half-Life! (Not Half-Life 2). Earth Special Forces is only for Half-Life 1, and will not work with Half-Life: Source, Half-Life 2, Counter Strike: Source and Day of Defeat Source.