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.
Assuming that the server is standalone and not a member of a domain, then you can achieve the result you desire by performing any of the 3 options below:
All steps above are detailed here. Please note that the link is a post on my blog.
If the server is a member of a domain enable the same policy in a GPO (Group Policy Object) and apply it to the relevant server(s) then run gpupdate /force on the relevant server(s) or reboot them to effect the change.