Windows 8 Metro acts like it's an extension of the Windows Start button. Once the start button is clicked, the user is taken to Metro, where they find tiles that allow them to access applications. While Metro apps keep the user within Metro and use the WinRT runtime, desktop applications take the user back to the desktop, where the old school Win32 is still used as the runtime.
The Build 2011 conference last week was filled with news releases and information, but once the dust settled, more details emerged about the upcoming Windows 8 OS. Although the OS is still in its development stages, it's apparent that Windows 8 is made up of two distinct parts: Metro and Desktop.