EDIT: Huh... Slowing it down to a crawl on the computer does almost nothing for it.
In your OS, do you have slowed down both mouse speed and acceleration? Or maybe that touchpad may have additional drivers that control it using a different interface?
And even setting it to the minimum from the OpenArena menu does not work?
In my OpenArena Q3config.cfg file, I can find these variables that seem mouse-related:
seta cl_mouseAccelOffset "5"
seta cl_mouseAccelStyle "0"
seta cl_mouseAccel "0"
seta sensitivity "14.950000"
You may try changing them... but write down your values before...
Another chanche may be this one... take a look to this section:
(
DO NOT LINK) h t t p s : / / openarena . wikia . com/wiki/FAQ#The_game_switches_from_fullscreen_to_windowed_mode_and_the_mouse_becomes_unusable
The first things there are about Linux, but then there is a thing that applies to Windows (in case one changed the screen's DPI to change font sizes)...
(Uhm... maybe that part of the help could be rearranged to make it a bit more visible? And I don't know if it is related with switching from fullscreen to windowed or not)