DirectInput mouse support is available with m_directinput 1. This will give a much smoother mouse response and completely fixes the issue of mouse acceleration on Windows 2000 or higher. You may need to play with the sensitivity cvar after turning on DirectInput as it samples slightly differently. If you don't wish to use DirectInput, m_fixaccel exists to enable the somewhat-ineffective mouse acceleration fix for Windows 2000+. With DirectInput, MOUSE1 through MOUSE8 can be bound, without DirectInput, up to MOUSE5. You can also use m_directinput 2 to enable "immediate" sampling mode with DirectInput if you have issues with m_directinput 1. The mouse behaviour when switching in and out of Q2 with Alt+Tab is also fixed so that it won't keep snapping your mouse all over the place.
From R1Q2 readme.
