If I understand the question, you want the three fields in the logon window to be the same.
The domain name should not change unless the users log onto different domains. If this is true, you might want to train them to use their UPN name rather than specify a domain. The user can enter "firstname.lastname@example.org" and a password.
The username can be forced to a blank with a group policy. You can do this with the Default Domain Controllers policy. (Logon policies apply to domain controllers, who then enforce them on their clients via a Privilege Access Certificate (PAC) in the Kerberos ticket-granting tickets it issues.)
1. Open the Group Policy Editor for the Default Domain Controller policy and drill down to Computer Configuration | Windows Settings | Security Settings | Local Policies | Security Options.
2. Find the Do Not Display Last User Name policy.
3. Check Define This Policy Setting and then Enable the policy.
4. At the client, either shutdown and restart or run secedit /refreshpolicy machine_policy.
This was first published in April 2001