Hyper-V Server 2008 Configuration

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http://serverfault.com – I need to set-up Lync on a Server 2008 machine. The problem is that Lync cannot be set up on a Domain Controller. That means I need to have one Server 2008 that's a domain controller and another that's Server 2008 running Lync. I figured the best way would be hosting it on a single machine, using virtual machines. I installed Server 2008, but now my question is this. Do I add two virtual machines (Domain Controller and Lync), or do I only add one virtual machine for Lync, and the 'parent' Server 2008 can act as a domain controller? (HowTos)