My HP uses a Synaptics Touchpad, and disabling the driver installation at boot would probably work.
In my TouchSmart it was even easier than that. Synaptics has a tab in Mouse Properties and then you can Enable and Disable the Touchpad in there. However, my TouchSmart also has a physical switch at the top of Touchpad, so using that is even easier and
more reliable. ; )
What I had started looking at is controlling devices using WMIC. If that idea could work even if the device is getting re-enabled (how?) we could put the WMIC command into Startup and control it that way.
In fact, the how? question could be investigated by running ProcMon for its Boot Logging option.
But the really dumb thing to disable is the Tap to click option. That shows up when the Synaptics icon is in the Notification area and right-click is done on it. What were they thinking? They don't even have a visual touch indicator so how can anyone
know what they would be "tapping" on?