This guide provides recommendations and cautions for running domain controllers as guests on Hyper-V servers. With Hyper-V, its possible to install multiple domain controllers on a single host server running Windows Server 2008. You can effectivel host multiple domains, multiple domains, multiple domain controllers for the same domain, or even multiple forests on one physical server. This can be very helpful in testing of a large-scale Active Directory deployment.

Running Domain Controllers in Hyper-V -