Download ESF 1.2.3. Install in half life directory, C -> programs file -> Half Life no steam -> ESF = In case of half life no steam (how ever, if you playing half life no steam you can't create lan game) Remember it is ProgramsFile/Halflife no steam/esf, and not only Programsfile/HalfLife
Steam half life = C-programsfiles-steam-steamapps-common-halflife-esf. Remember that the installer must to be common/Halflife/esf, and not only common/halflife.
^^^
To me is common, but it can be your nickname of steam. if not both, than its a directory where you have half life's directory inside