Go to the registry key:
HKLM\Software\Microsoft\W indowsNT\CurrentVersion\Winlogon\SpecialAccounts\U serList

Create a new DWORD, setting its name to the name of the account you wish to hide. Then set its value to 0 to hide it. However, this account isn't completely hidden because it is visible to administrators in Local User and Groups and also the profile is visible in the Documents and Settings. When you are at the welcome screen, and you want to login to this account, then press Ctrl+Alt+Delete twice and it will display the log-on promt style similar to Windows 2000, then type the username, and the password and hit enter.