girly i don't understand how the person was able to log into your computer. actually i find it impossible they did this to you using remote assist. they would need not only the external address, but also they would have to know your username and pass. and as a second layer of security the intruder would have to wait for you to accept his request to take control of your computer.
are you sure this wasn't someone in your family (who knows your user & pass) playing a trick on you? the only way to do what you say is through remote desktop, which still requires knowledge of your winXP pro username & pass. also remote desktop is not enabled by default.
i think nobody was "hacking" you, maybe you left your webcam on. microsoft would not be stupid enough to leave a security hole this big on winXP, cmon now