I no longer work at Microsoft, so please don't bother leaving a comment here or trying to contact me through my MSDN blog.
You can find my new blog at http://www.technologytoolbox.com/blog/jjameson. My new site also provides copies of all posts from my MSDN blog.
In a previous post, I noted how the "Jameson Datacenter" (a.k.a. my home lab) currently runs two domain controllers (DCs) on a couple of VMs.
If you choose to virtualize one or more DCs in your environment, make sure you are aware of the considerations, risks, and recommendations detailed in the following TechNet guide:
This appears to be the most recent version of the document that I used when setting up my environment.