"A free utility that closes Winamp or shuts down the PC after playing a set number of tracks."
Kill Winamp is a plug-in for the Winamp player, completely free, that acts as a timer. Kill Winamp stops or pauses Winamp when a set number of tracks has been played, or when the pre-established time has run out.
There is also an option to shut down the PC when the timer runs out, either shutting down the operating system or killing power to the system if the hardware allows it. Kill Winamp is a completely free tool and one that doesn't take up much space: just half a mega in size.