disable trackpad on E6500 running vista?

when im typing, and my palm accidentally touches the trackpad, the pointer will jump and i start typing somewhere else, but usually i don't realize this until way too late, any idea on how to disable the trackpad? I've tried control panel (classic view) > Mouse Properties > Hardware Tab > Properties > General Tab > Change Settings > Driver Tab, and there is a disable button, but it is greyed out. Help Please ?!