Disable mouse acceleration
As far as I know, there is no way to do this without external tools.

Usb Overdrive lets you do this http://www.usboverdrive.com/ and is what I use.

Steer mouse also has this setting. http://plentycom.jp/en/steermouse/  

Mouse Curves http://triq.net/articles/mouse-acceleration-preference-pane-mac-os-x  Has the advantage of being free, but Apple removing the acceleration API in 10.6 may have ramifications on its utility.