Are you using the Synaptics driver in your xorg.conf?
If so, try adding this to the mouse config in your xorg.conf, this will turn off horizontal scrolling
Code:
Option "LeftRightScrolling" "off"
Option "HorizScrollDelta" "0"
For sensitivity try playing with the MaxTapTime variable
Code:
Option "MaxTapTime" "180"
Check out the man pages for "synaptics" and "synclient"