if you dont want to use touchpad at all or for a while. Open up the palmrest and  un-hook the connector.

If you never use the touch-pad, you can disable it in the BIOS (press F2 at start-up and change the pointing stick to ps/2 mouse, or serial mouse depending on what you have)

That won't work if he is using a USB mouse or track point.

Look for it in Mouse Properties. You need to install Dell driver to have this feature.