Does the DHCP message appear on the host, or on the client during the OS install? If you can, please provide the full text of the message. The host should still have it's original internet connection settings, and the loopback adapter will be an additional connection.
If the DHCP message appears on the virtual client during the OS install, then specify the IP address rather than using DHCP which assigns it automatically. Choose an address in the same IP range as the host (pp. 36-37).
Note that you can create and configure the client VPC's loopback adapter after the OS is installed. It's preferable to do it before making the machine a domain controller if only to save the steps and risk of changing the IP address afterwards.