Running "Poke646: Vendetta" without Steam is not recommended, as it produces some graphical glitches. It is fully playable though, so if you need to run "Poke646: Vendetta" under the original non-Steam Half-Life, here's how to:

Make sure you have the original Half-Life and Patch 1.1.0.8 or higher installed.

Download "Poke646: Vendetta" v1.0 and run the installer. When being asked where to install the game, click the "Browse" button and place it in the directory where you installed Half-Life (for instance "C:\SIERRA\Half-Life").

Start Half-Life and you should be able to select "Poke646: Vendetta" from the "Custom game" menu. Once selected, don't let the unchanged menu graphics fool you, "Poke646: Vendetta" is loaded and fully functional.