There's usually a way to turn the trackpad off, though exactly where will depend on the drivers. Have a poke around in mousy settings, or devices.
USB meece are a case of plug them in and they just work (if you have multiple pointing devices, the pointer gets the sum of their inputs[1]). Again, the usual settings to adjust speed, button behaviour etc, which should be independent of the trackpad.
[1] For example, on this machine I have a mouse for my left hand and a trackball for my right. If I move them both at once I can wrestle with the position of the pointer.