Enabling Windows Vista “hidden administrator” and password-protect its Windows XP equivalent

To disable this administrator account, follow the steps above to return to the Command Prompt in administrator mode, type net user administrator /active:no, press Enter, type exit, and press Enter again.

Give XP's hidden administrator account a password
This administrator account is a well-documented security risk in Windows XP because by default it doesn't have a password, which means anyone can log into your system via this account, change the passwords for all the other accounts, and perform other mischief. To give the account a password in XP Home, restart the PC, press F8 before Windows loads, select Safe Mode, and press Enter.

The only selection will likely be Microsoft Windows XP. With this option highlighted, press Enter again. You'll see a Welcome screen with an account labeled Administrator. Click this account, choose Yes at the warning, open the User Accounts applet in Control Panel, click the Administrator account again, choose Create a password, enter the new password twice, enter a hint (if you wish), and click Create Password. You may also be asked if you wish to make this account's files private. Make your selection and click Finish.

There's a much simpler way to make this administrator account visible on the Welcome screen in XP Pro: Open the Tweak UI Powertoy, click Logon in the left pane, check Show "Administrator" on Welcome screen in the Settings window on the right, and click OK. Note that you'll still have to log into this account and follow the steps above to add a password for it.

Select the Logon option and check this option to add the hidden Administrator account to the Welcome screen in XP Pro.