When the Windows PE phase of Windows Setup is running, you can break into a command prompt window running under Local System context by pressing SHIFT+F10. This is cool because it lets you view Setup logs and run commands like regedit, diskpart, robocopy and other stuff. And you can even do other neat stuff like popping in a USB flash disk that has some additional tools on it you want to use.
On the other hand, if you’re an admin deploying Vista workstations in an enterprise, you may not want users to break into a command prompt when Windows PE launches on their computers. Fortunately Microsoft also provides a way for you to prevent this from happening, see KB 929839 at http://support.microsoft.com/default.aspx/kb/929839 for more info.
For more information on deploying Vista, see my series of articles on WindowsNetworking.com starting with http://www.windowsnetworking.com/articles_tutorials/Deploying-Vista-Understanding-Windows-AIK.html.
Mitch Tulloch was lead author for the Windows Vista Resource Kit from Microsoft Press, which is the book for IT pros who want to deploy, maintain and support Windows Vista in mid- and large-sized network environments. Mitch was also the author of Introducing Windows Server 2008 and technical project lead for the Microsoft Office Communications Server 2007 Resource Kit, both books also from Microsoft Press. For more information on these and other books by Mitch, see www.mtit.com.