For file sharing purposes I have always had at least one hidden account on my computer. Currently I have one that I use to connect my Linux box to my Windows 7 box, and a second for allowing friends to copy MP3s and Movies off my drive when I go to lan parties. Unfortunately, when you create an account for sharing purposes Windows will automatically add it to the login screen. Since this not only causes clutter on our login screen, but a security threat as well, I will show you how to remove this user from the list.
The process for hiding an account has not changed since Windows XP. This involves tweaking the registry so I do not recommend proceding if you are not comfortable doing so. To access the registry editor, select Start->Run or hold down your Windows key and hit R. In the next prompt, enter regedit and hit enter.
Navigate to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon and create a sub-key named SpecialAccounts if it does not already exist. Inside of that key you will create another called UserList. Make sure UserList is selected and on the right hand side right click and select New -> DWORD (32-bit) Value. Give this new value the same name as the user account that you would like to hide.
To confirm that it worked hold down your Windows key and hit L which will lock the computer. If you see the user in your list then lock back into your admin user and double check your configuration. If not, then you have successfully hidden it.
To make this process a little more simple, you can create a text file will the following contents and save it with a .reg extension. This is very handy if you need to do it on serveral computers or if like myself you have many registry tweaks you need to apply each time you reinstall Windows.
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList "lan"=dword:00000000
In this example I use lan as the username, you can of course use whichever username you like just make sure to update the value in the DWORD value. After saving this file you can simply double-click the registry file and it will automatically apply it for you.
In the event that you would like to log into this user you can activate the old Pre-XP login screen by hitting CTRL+Alt+Del at the login screen. You will be prompted for a username and password, enter the appropriate values and hit ok. Keep in mind this will create a desktop profile for the user the first time you log into it, so the first time you do this it may take a bit longer.