Disabling the Synaptics Touchpad driver in Linux (tested on Ubuntu Feisty)

1) Edit /etc/X11/xorg.conf and add the line
Option "SHMConfig" "true"
to the section that configured the Synaptic Touchpad driver.

The result should be something like this:

Section "InputDevice"
Identifier "Synaptics Touchpad"
Driver "synaptics"
Option "SendCoreEvents" "true"
Option "Device" "/dev/psaux"
Option "Protocol" "auto-dev"
Option "HorizScrollDelta" "0"
Option "SHMConfig" "true"
EndSection

2) Install gsynaptics by running
apt-get install gsynaptics
as root

3) Restart your X server (if you don't know how to do this, just restart your laptop)

4) Start gsynaptics and configure the touchpad:

You can also disable vertical scrolling by going to the scrolling tab.