ESF will NOT work with any game other than Half-Life 1
1.
Download Steam.
2. Run the .exe file you just downloaded to install Steam and let it update completely. You will need your CD-Key from the back of your Half-Life 1 case.
3. When Steam is finished updating, turn it on.
4. Under the "Games" selection in the Steam toolbar, select "Activate a product on Steam..." and input your CD-Key.
5. Once your CD-Key is authenticated, download Half-Life 1 from Steam and let it update completely.
6. Once that is done,
run Half-Life 1 once. If you don't run it at least once,
you will not be able to install ESF
7.
Download ESF v1.2.3 full installer.
8. Run the installer.
9. It will point to the correct directory for you, so just hit install. The directory should look
somewhat like this :
C:\Program Files\Steam\SteamApps\
Your Account\half-life\esf
10. ESF should now appear in your games list.
11. Double-click and enjoy!