During the install process you will come to a screen that will ask if you want to do a custom install. Choose that option. Another screen will come up asking where you want to install the game. When I installed, I just chose to install the game on my C drive.
During installation a folder was created on my C drive with the title "Bethesda Softworks". Within this folder was the Fallout sub folder. This will place the program outside the User Account Control and allow you to play without having to open the game as an aministrator each time you want to play.