A. During the Windows PE (WinPE) portion of the OS installation (which is the initial part), if you press Shift-F10, a command prompt will open, as the figureshows.
This key combination works only after the installation process has started (i.e., you need to have clicked to Install Vista on the initial dialog before the Shift-F10 will function). From this command prompt, you can perform functions that might not be possible during the actual installation process (e.g., advanced DISKPART functions). Use this method cautiously and avoid making too many changes; the installation process usually knows best.