This is the best way to remove mouse acceleration on Mac Os X:
In your terminal(terminal is located in Applicatons/Services/Terminal):
macpro:~ user$ curl -O http://ktwit.net/code/killmouseaccel
macpro:~ user$ chmod +x killmouseaccel
macpro:~ user$ ./killmouseaccel mouse
It was copypasted from here.
I write it here just in order not to loose such a useful recipe.