How to hide user accounts in Windows 7

Run regedit and go to the key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
If this key does not exist then you must create it.
Create a DWORD value with the name of the user you want to hide and assign 0 to this value.
If you want to show the user again in the login screen change the value from 0 to 1.