Well i can see from the tags that you probably have a Sony laptop but know the make and model would help me in the case but from not knowing that i would say to go to your control panel from your start bar, then go to mouse,Click on Device settings. Your Touch pad should show up there in the Devices listing. then click the device now you should be able to click the disable button, if for some reason its not showing up then i would check in your device manger, but the only option you would have there would be to disable/uninstall the driver. Also another thing this is were the make and model of laptop would help me but a majority of laptops have hot keys to turn off the touch pad for that vary reason of miss keying, i think the default is FN(function key) and F7. I hope this helps.
Regards Zakk