From Nonecks Docs

1. Open your xorg.conf file for editing as root

gksudo gedit /etc/X11/xorg.conf

• Find the Synaptics Touchpad InputDevice section, it should look something like this:

Section "InputDevice"
          Identifier      "Synaptics Touchpad"
          Driver          "synaptics"
          Option          "SendCoreEvents"        "true"
          Option          "Device"                "/dev/psaux"
          Option          "Protocol"              "auto-dev"
          Option          "HorizEdgeScroll"       "0"
          Option          "TapButton1"            "0"
EndSection

• Add this line right before EndSection:

          Option          "TapButton1"            "0"

• Save the file, then log out and log back in