The only method to validate is to hire a hacker, get very acquainted to sniffer to monitor access, or a site that will query your protection.
You state that you are running XP, do you have a domain server that you validate to? If you do and are diligent on the rights you are ahead.
Also, there are some key Logins that you always want to limit or remove access.
IWAM_, IUSR_, and guest accounts. These are
really easy hack points. The other things to look for are users and built-in spy ware applications that can be exploited. HP, Maxtor and a few others have CDAEMON enabled to info back to the manufacturer. Also, applications like RealAudio, Kazaa, and the likes, all are open doors waiting for someone to enter.
Doug