virtualbox.org

Hey everyone, I'm fairly new to VM's, networking, etc etc, so don't fault me for trying to learn if this may seem like an easy question to answer: What are the correct network configurations needed for the Server VM (Win Server 2008 R2) and the Client VM's (Win 7) to be able to join the client's to the domain? I've tried pinging the server from the clients, with no response. Any advice?

That really doesn't have much to do with VirtualBox. To set up a simple domain like that, the client machine must be in the same network as the DC an use the DC as its DNS server. How you set that up in VBox is up to you. I always use internal, but you need to know a bit about networking to get Internet access working. This is not a VirtualBox problem but an AD one. You have the same thing on physical networks with physical machines

If you are not interested in Internet access for the vms, put them in an internal network. Give the DC a static IP in its own IP subnet and run dcpromo. Let dcpromo configure DNS for you. Give the client an IP address in the same IP subnet as the DC and use the DC's IP address for its DNS setting.