What can we possibly add about Microsoft that has not already been discussed and analyzed to death?
Greg Scott with Infrasupport holds an MCSE (Microsoft Certified Systems Engineer) certification and has done dozens of Active Directory and Exchange deployments over the years. Infrasupport is currently deploying several Windows Server systems as virtual machines in a RHEV (Red Hat Enterprise Virtualization) environment.
Because this is the best way to provide high availability without breaking the bank. Purchase a Windows Server 2012 Standard license and it comes with right to operate two virtual machines in the same virtual environment. This is a perfect combination for a small business Exchange Server and Domain controller tandem.