If you move a workstation from one domain to another, the new domain may not show up at logon in the domain drop down list. Instead, the old domain and its trusted domains show up. You can avoid the issue by moving workstations into a workgroup and then into the new domain. This automatically clears domain info from the registry. But if you have the problem, it is easily resolve by deleting the following registry value and rebooting. NT will recreate the correct domain list at reboot.

Hive: HKEY_LOCAL_MACHINE
Key: Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Name: DcacheUpdate

If you are concerned about registry editing, you could use the workgroup approach instead.