This is a small tip on how to bring up a Command Prompt window while Windows is installing. I have tested this solution on Windows 7, Windows Server 2008 R2, Windows 8.1 and Windows 2012 R2, but it should work on every operating system newer than Windows Vista or Windows Server 2008, including them.
Using this method you can open a CMD window during the first part of an installation, in WinPE, and also after the restart, until Windows is fully booted up (with some exceptions).
The keyboard combination that opens the Command Prompt is: SHIFT + F10
This works for example after booting from CD/DVD/USB up until the computer restarts.
After that you can use this method during the Installing drivers phase or The setup is preparing your computer for first use phase. This is very cool as you can troubleshoot failing device drivers for example.
Another time during the installation when I found this method useful is near the end when in Windows 7 for example you are asked to specify a user name or when in Windows Server you are asked to choose an Administrator password. For the client OS it is especially useful as you can run Sysprep without creating a user account.