Is the "message board" a monitor? a TV with VGA? a TV with HDMI? Some sort of serial / usb connected device? Give us some clues.
What we've a LOT of success with is using a TV with HDMI and attaching a RaspberryPi running "Screenly
At the moment we have it pointed at a URL showing phone system stats but in the past we've had it rotating between images uploaded to the Pi.