The Touchpad on my Dell laptop is an annoyance; while typing, if I inadvertantly strike
it, the "I-beam" (or Mouse Pointer) ends up somewhere other than where I want it.
None of the settings I have tweaked thus far will kill the touchpad.
Actually, the best way I found is to open Terminal and type:
Your touchpad should show up in there somewhere. Make note of the touchpad's full name. Then, in your Startup Applications, make a new entry and put in:
Where I have ETPS/2 Elantech Touchpad, put in the full name of your touchpad and save it. Make sure the touchpad's name is wrapped in quotes. Now every time you log into Ubuntu, the touchpad will be disabled. You can uncheck it in Startup Applications to stop this behavior or run that command in terminal with a 1 instead of a 0 to enable it again.
Try installing the Synaptik touchpad manager from Ubuntu Software Center. It has the option to disable touchpad while typing...and many more options.