try some of these from http://www.kellys-korner-xp.com/xp_wel_screen.htm
Hide Users from the Welcome Screen
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserLis t.
Note: There is a space between Windows and NT.
Add the username you wish to hide as a DWORD value. Set the value to 0 (zero). This will prevent the user from showing up on the welcome screen. You will need to press CTRL-ALT-DEL twice at the logon screen to get the old Win2K logon, to be able to logon to the account you've hidden. Adding a username and setting the value to 1 will cause that user, such as Administrator, to show up on the Welcome screen as well.
TweakUI Option to Remove Users from the Welcome Screen:
About/Policy/Run Group Policy Editor/User Configuration/Administrative Templates/Start Menu and Taskbar/Remove User Name from Start Menu.
A User Account Does Not Appear in the User Accounts Tool or the Welcome Screen
An existing user account may not appear in the User Accounts tool in Control Panel, or on the Welcome screen. You may also receive the following error message when you attempt to create a new account:
The account already exists
This behavior occurs because you have disabled the account. Disabled user accounts do not appear in the User Accounts tool, or on the Welcome logon screen. You can only access these accounts in the Local Users and Groups snap-in.
To resolve this behavior, first determine whether an account is not active:
1. Click Start, right-click My Computer, and then click Manage.
2. Expand the Local Users and Groups node.
3. Click Users.
If the user account is displayed with a red X through it, it has been disabled.
To enable the account:
1. Double click the account.
2. Click to clear the "Account is disabled" check box.