Automatic Administrator Login:

Well here's the trick which you can use to prove that Windows XP is not at all secure as multi-user operating system. Hacking the system registry from any account having access to system registry puts you in to the administrator account.
REGEDIT 4
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
"AutoAdminLogon"="1"

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