When I logon to Windows 2008 via the console or via RDP it shows me the names of user accounts already created as clickable buttons.
How do I prevent this and make Windows 2008 ask me for a username that must be typed?
You should be able to set this in the group policy editor (Run: gpedit.msc) under:
Computer Configuration > Policies > Administrative Templates > System > Logon
Set it to use the classic login screen. This will work if the server is standalone. If it is part of a domain, it will follow this policy as set by the domain policy instead.