I wrote an article on my personal/tech blog about how to build a domain controller for use in a disconnected development lab. This is also relevant for .Net if you're building an Active Directory connected app, so, here's the beginning of the article and a link:

“I answered a question with regards to Active Directories today whose answer is very complex compared to NT4. On NT4 if you wanted to build a dev lab, you'd make a BDC, disconnect it from the production network, move it to the lab, promote to PDC, and then delete the BDC account on the production network.

On an Active Directory, this procedure is comparatively complex! This scenario is a pretty common question, I imagine, so here goes the step-by-step...“
http://www.briandesmond.com/blog/posts/251.aspx