Note that Half-Life 1 can be interchanged with CS 1.6, and DoD.
ESF will NOT work with Condition-Zero packs
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.
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\
Your Game\esf
10. ESF should now appear in your games list.
11. Double-click and enjoy!
If you are still having trouble please refer to the Frequently Asked Questions sticky.
Thanks to Karrde for this information.