Create one? I don't know but I found a free software download that will sound an audible alarm if a wrong password is entered: http://wareseeker.com/Security-Privacy/predator-22.214.171.124.zip/7d80d8dd2 A word of caution, I've never used this software and I didn't do any research on it. If you decide to give it a try, be sure you properly research it for effectiveness and bugs, then scan it for spyware, viruses and malware before you install it. Treat it as a hostile program until you are satisfied it will do no harm.
If you are good at programming, you could create a log-on program, embed that deeply into the startup functions so that it is very difficult to remove. Have it start up every time XP starts. If the wrong password is given then it gives the alarm and waits for you to come and hit your little brother up side the head. If the right password is given it lets you in and waits until the next reboot. The deeper it is hitdden in the startup system the harder it will be for someone to break it.
You're unlikely to get a solution by asking the same question again, if you're not able to hack Windows and re-write software you're out of luck I think.www.instructables.com/answers/how-can-you-create-an-alarm-on-vista-logon-If-you/ L