To disable the touchpad, trackpoint or touchscreen of a laptop, use the tool xinput to list the devices currently known to the X window system.

blu@aptenodytes:~$ xinput list
⎡ Virtual core pointer                            id=2	[master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer              	id=4	[slave  pointer  (2)]
⎜   ↳ TPPS/2 IBM TrackPoint                   	id=10   [slave  pointer  (2)]
⎣ Virtual core keyboard                   	    id=3	[master keyboard (2)]
    ↳ Virtual core XTEST keyboard             	id=5	[slave  keyboard (3)]
    ↳ Power Button                            	id=6	[slave  keyboard (3)]
    ↳ Video Bus                               	id=7	[slave  keyboard (3)]
    ↳ Sleep Button                            	id=8	[slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard            	id=9	[slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                  	id=11   [slave  keyboard (3)]

Now from the list of devices, take the id you wish to disable.

user@host:~$ xinput set-prop 10 "Device Enabled" 0

To enable a device again, use a 1 instead of 0 as last argument:

user@host:~$ xinput set-prop 13 "Device Enabled" 0