Though you can’t truly run metro-style apps in the desktop interface, you can snap them to the right or left side of the screen and then have the remaining portion of the screen for the desktop interface or another metro-style app.
Example of a metro-style app snapped to the right side.
When using a metro-style app you can hit Win + . to toggle snapping to the right and left side. Or with touch, swipe in slowly from the left.