Overview
This guide will help you with the annoying mouse acceleration, so you can enjoy New Vegas without having to deal with it.
Introduction
Now someone else may have already made a guide on this, but I wanted to post it here just in case.
So recently, I started playing New Vegas, and the mouse acceleration really got to me, so I found a way to fix it.
How to fix it
Go to your New Vegas install directory (this varies, but the default location is in the steamappscommon folder), and find Fallout_default.ini. Open it using notepad, and scroll down to the section titled [Controls].
There, paste the following:
fForegroundMouseAccelBase=0
fForegroundMouseAccelTop=0
fForegroundMouseBase=0
fForegroundMouseMult=0
Then, just open the game and enjoy.