Open a Terminal from Applications -> Accessories -> Terminal
Type sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf_synbackup
Type gksudo /etc/X11/xorg.conf
Enter your password if it prompts you.
Search for a section that looks like the following
Identifier "Synaptics Touchpad"
Add a line above the End Section line and put this into it:
Option "SHMConfig" "on"
Save the file and close gedit and the terminal window
Now you need to restart your desktop GUI using Ctrl-Alt-Backspace
Add the Startup Command
Open the sessions manager: System -> Preferences -> Sessions
Click the far right tab labeled Startup Programs
Click the Add button
Type in the following: syndaemon -i 1 -d
Hit ok then hit close
You can restart Gnome with the Ctrl-Alt-Backspace
To disable the touchpad completely, open your xorg.conf, and comment out or remove the line that says
InputDevice "Synaptics Touchpad"
in the "ServerLayout" section (it's near the bottom).