When you add an account for certain users with Windows XP, their user names will appear on the Welcome Screen. Sometimes a user needs to be added to a Windows XP machine, because he needs access (via the network) to resources on the machine, but he will not be physically logging in on the computer. You can remove his name from the Welcome Screen, while still maintaining the user account.

Start the Registry Editor
Go to HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ Winlogon \ SpecialAccounts \ UserList \
Right-click an empty space in the right pane and select New > DWORD Value
Name the new value exactly as the Username
Leave the Value data as 0

If you want to enable this user again on the Welcome Screen, either double-click the Username value, and change the Value data to 1, or delete the Username
Close the registry editor