Download Half-Life 1 from steam, then launch Half-Life 1 once and in the Half-Life menu, quit the game. Once you have done that, the "grey' button in the Earth Special Forces installation will be click able. It's required that you have to launch either Counter-Strike or Half-Life once before the ESF Installation can detect Half-Life. If the button is still grey, then Launch Half-Life 1 and start a new game. And then quit the game and try the installation again.
How? When you launch Steam and login on your account. You should see "Half-Life" in the game list, double click on it to download the game. Once you done that, do the instructions i gave in the second post on this thread or read the sticky threads for more help.