If an audio file is currently playing by Windows Media Center, and then Windows Media Player is opened, the latter player automatically plays the same audio file playing by the first player.
Any notebook system running Microsoft Windows Vista.
You cannot play one audio file by Windows Media Center and another different audio file by Windows Media Player simultaneously.
While both of the players are playing the same audio file, control actions whatever done in one player are also reflected in the other, such as changing to a new audio file, pausing and stopping current audio file. This is a limitation of Windows Vista.