Steam:

Drag & Drop The .esp To: Program/Steam/Steamapps/Common/Fallout New Vegas/Data

Start Fallout New Vegas Using The "Play" Button, Then Click "Data Files" In The Launcher And Check "Mojave Sniper Post.esp".

Non-Steam:

Drag & Drop The .esp To: Fallout New Vegas/Data

Open FalloutNVLauncher.exe, Then Click "Data Files" In The Launcher And Check "Mojave Sniper Post.esp".