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"

Not only this option but you will find many more option in this registry path like changing default user name,auto start of windows shell (by default explorer.exe),option to change the windows default shell.