Windows Operating system allows user to create multiple user account to display in login screen. But you can hide a perticular user account or you can create a Hidden user account.
First you have to create a User account to make it Hidden in Login screen. (follow the steps below for Windows Vista and Windows 7)
Control panel > User Account and Family Safety > Add or Remove User Account

If you already have an existing user that wants to be Hidden from login screen , then follow the guide below.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
Note : If SpecialAccounts and UserList is not found, create new sub-key.

For example : if the user account is WinSpark, then registry value should be WinSpark.
To display the user account on Welcome Screen again delete the registry entry, or set the value data to “1″.
To login into Windows using an user account that has made hidden and invisible, just press Ctrl+Alt+Del to bring up Windows Logon dialog, and then type in the user name and password manually.