One way to practically prove that the NT 5.2 kernel uses preemptive multitasking instead of cooperative would be if a compiled program had an infinite loop that the operating system doesnt crash. This means that basically because of the use of time-slicing in preemptive multitasking we can still use the operating system while the infinite loop is running. If the NT 5.2 kernel was using cooperative multitasking the operating system would crash seeing how it would have to wait for that process to finish before moving onto another process. That fact that the operating system does not crash proves we are using preemptive multitasking.