Bob see here:
The built-in Administrator account is hidden from Welcome Screen when a user account with Administrator privileges exists and enabled. In Windows XP Home Edition, you can login as built-in Administrator in
Safe Mode only. For XP Professional, press CTRL+ALT+DEL twice and input your Administrator password in the classic logon window that appears.
There are some ways to enable showing administrator account in Windows Home Edition welcome scren as well... first one is to use TweakUI v2.10, and click on "
Logon" option in the left pane, then put a checkmark against the option "Show Administrator on Welcome Screen".
Second one is editing registry:
1. Start the Registry Editor [Regedit.exe]
2. Navigate to the following registry key:
[HKEY_LOCAL_MACHINE
\SOFTWARE
\Microsoft
\Windows NT
\CurrentVersion
\Winlogon
\SpecialAccounts
\UserList]
3. Use the File, Export option to backup the registry, in case.
4. Right-click an empty space in the right pane and select New > DWORD Value.
5. Type-in Administrator as the value. Double-click this new value, and enter 1 as it's data
6. Close the registry editor
You may use this procedure to hide/show users in the Welcome Screen for any user account. Type the account name accordingly in step 5.
I also found this:
NOTE for Windows XP Home Edition users: While you can configure Windows XP Home Edition to show Administrator account in the Welcome Screen, you cannot login as Administrator in Normal mode. Boot into Safe Mode to login as Administrator. Please see the following Microsoft Knowledgebase article:
Error Message:
Unable to Log You on Because of an Account Restriction[Windows XP Home Edition]
http://support.microsoft.com/?kbid=290109