For a home PC, needing to log on every time your PC starts up may not be necessary. This hack will describe how to have your PC log on to Windows automatically. If you are concerned about security, you should NOT apply this hack.
- Click the Start button and then click Run.
- In the Run box, type 'control userpasswords2' (without quotes) then click OK.
- Clear the "Users must enter a user name and password to use this computer" check box, and then click Apply.
- In the Automatically Log On window, type the password in the Password box of the user account you will use for auto logon, then retype the password in the Confirm Password box.
- Click OK to close the Automatically Log On window, and then click OK to close the User Accounts window.
- Restart your Computer to test auto log on.
How to manually set up of registry
•Using RegEdit, navigate to the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
•Create or Open and fill the String Type value of "DefaultUsername" with the desired username.
•Create or Open and fill the String Type value of "DefaultPassword" with the desired password.
•Create or Open and fill the String Type value of "AutoAdminLogon" with the data "1".
To set up de desired DomainName, modify the data from value "DefaultDomainName"
Link:
http://www.wikihow.com/Enable-Automatic-Logon-in-Windows-XP