m_mouseaccel1 "0"
m_mouseaccel2 "0"
m_filter "0"
m_customaccel "0"
m_customaccel_max "0"
//cl_mousespeed "0"
//m_rawinput "1"
Throw those into your autoexec.cfg
And use this (http://donewmouseaccel.blogspot.com/2010/03/markc-windows-7-mouse-acceleration-fix.html) to remove acceleration from Windows 7/8/8.1. Uncomment the last 2 lines for use in the newer engine.