First of all uninstall half-life. Then, install it and download
Steam. Install steam as well and run normal half-life (through steam ofcourse) once so the half-life folder in the steam folder will be created.
Then, install ESF 1.2 and after that patch 1.2.1, then Select Earth's Special Forces from your desktop (or if id doesnt create a shortcut, select "play games" in steam menu and select esf under "third party games")
Hope i helped you