The welcome screen displays all of the local users on the system, except the built-in administrator account that was created during setup.

Hide Your User Account

If we want to hide a specific user from the list, we need to create a special value under this registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows
NT\CurrentVersion\Winlogon\SpecialAccounts\UserList

Under this key you simply create a new DWORD value – the name matches the users name exactly, and the value is one of the following (Decimal format)

0 – Hides the user just from the welcome screen
1 – The user is shown

Before you start putting values in this key, I want to warn you. This tip is particularly dangerous. If you make the wrong move, you could make it nearly impossible to get back into your system. (Use safe mode if you mess up, to get back in)

To disable the users I want, I browse to the registry key on my system:

Now I want to hide all of the accounts except my own, so I add each of the accounts shown on the welcome screen, and give them a value of zero.

How do you log on now that you are a hidden user?

If you are running windows XP Professional you simply need to press CTRL-ALT-DEL twice, and the standard logon screen will be displayed. This has one pitfall – it will fail to work if a user is still currently logged in. If you are having trouble getting it to show, then reboot and press it twice before any users have logged in. (I have not tested this in Windows XP Home…Some people say that the standard logon screen won’t come up (maybe they didn’t get all of the windows updates?), if that happens boot into safe mode and edit the registry back to normal)

SOURCE