be sure that you've run HL, CS or Steam before, then this tool should be able to locate your ESF path
if you've got DoD Retail, create a "REG_SZ" key named "InstallPath" with the HL-folder/Steam-HL folder as value in "HKEY_CURRENT_USER\Software\Valve\Half-Life\"
sorry ... I don't know any DoD-Retail user ... so I don't know what they're using
if you've still problems (or problems with my explanation) go ahead and ask here