Why don't you explain how you did it? I guess the maker of this mod would like to know and every other person having issues installing it with Half-life 1, but help yourself and move on...feel free.
I'll give this a try this a download and play through this week, due to the large amounts of positive comments, looking forward to it.
Oh and to play 3rd party Half-life 1 mods through Steam you should paste the mod folder into this directory - Steam/SteamApps/<account>/Half-Life directory. The next time you open the "My Games" list, it will be listed under "Third Party Games."
I did exactly what he told me to do. Just didn't restart Steam. When I did, it worked.