The Diagnostics and Recovery Toolset, is one of the tools in the Microsoft Desktop and Optimization Pack, DOP. When you boot a machine from a DaRT boot device, you get all the regular Windows Recovery Environment (WinRE) tools, plus several additional tools for things like resetting the local admin password, or recovering deleted files.
There're a couple key new things in DaRT 7, which was announced at MMS. One is support for PXE booting to a DaRT image, instead of requiring physical boot media. the other is the ability to remote desktop to a DaRT boot, so the helpdesk can now talk a user through a network boot into the DaRT environment, and then allow the helpdesk to take remote control of the machine to run the recovery tools.
Paul MacKnight goes in to this in more detail and gave me a demo of what it looks like.