In game's launcher, choose windowed. Max game (optional). Edit %USERPROFILE%\Documents\My Games\FalloutNV\FalloutPrefs.ini: iSize W & H yours (+ border = borderless). Edit (path-to-game)\Fallout_default.ini: iLocation Y & X (+ border & down&right by 1 pixel = borderless).
(PLP screenshot with bezel effect)
Remember file changes. If in-game settings changed, must redo.
View guide for general help with the instructions.