Exchange 2007 using Interim mode domain (not supported)

Exchange 2007 documentation it’s not clear about using Interim mode.

Active Directory Domain Functional Level set to Windows 2000 Native or greater

Iterim mode seems to be greater than Windows 2000 Native, but not.

Setting Interim mode doesn’t enable running Exchange 2007 setup. Readiness checks shows error: Active Directory domain “dc=demo,dc=com” is in mixed mode.