How do I set up an isolated network in vbox?

[Cancerous]

I need to set up a windows server and an email server, completely isolated so it doesn't interfere with the network where I work.

I also need multiple VMs to communicate to each other through this server.

Would internal networking be best for it? And how do I go about setting it up?

Thanks.

[Perryg]

The easiest and for most the best way to use and test Windows domains in VirtualBox
Setup Windows Domain in VirtualBox