Instructions
Highlight the "New Vegas" add-on pack files and press "CTRL" and "C" to copy them.
Open "Computer" from the "Start" menu, then open the "C:\Program Files (x86)\Steam\steamapps\common\fallout new vegas\data" folder.
Click inside the folder, then press "CTRL" and "V." This copies the add-on packs into the appropriate folder.
Start "New Vegas," then click "Data" on the startup menu. Select the checkboxes next to the names of the add-on packs you copied.
Play the game with the new add-on packs.