How would I go about setting up VirtualBox for this kind of environment?
Just like real-life servers work. Have one server that receives the outside internet connection, has all the DNS, DHCP, AD... stuff and all the client PCs connect to it. I am unable to get the server (Windows 2012) and client (Windows 7) PC connected internally.
How should I set up the adapters?
In the Network settings for both VM's you can select the 'Internal Network' option. Mkae sure the name matches for both VM's. For the server you obviously would need two network interfaces, one connected with NAT or bridge, and the other with the 'Internal Network' setting.
If you match the internal network names, you should only have to assign IP addresses (or make your server a DHCP server) and you're good to go.
-- Turned out the asker didn't disable the firewall. After disabling the firewall, connectivity was fine.
