I ran into this the other day and needed to set the localhost name to the default login. So you do the following but put the computer name in the domain field.
Q: How do I enforce the domain name in the logon dialog box?
Last modified: January 18, 2008
A: By default, the value for Domain/Computer in the logon dialog box is taken from the last logon that was used on the console. You can override this and force the correct domain name in the login box i Terminal Services Configuration:
Start – Administrative tools – Terminal Services Configuration – right-click RDP-tcp connection –
Properties – Logon Settings – select “Always use the following information”
Leave the User name and Password fields blank and enter the domain name you would like as the default in the Domain field.
Also make sure that you check the box for “Always prompt for password”.