If you want to play some tunes, feel free to use this PC along with the Kenwood stereo above it. You can play any of the songs downloaded onto it through media player, or you can take the audio cable out of the front (headphone jack) and plug it into your device.
If you want to put some of your music on it, just copy it to the music folder. The music folder should be shared on the network as well.
One thing though, during the business day (M-F, 8am to 5pm) don't play it to loud. The neighbors above can hear it through the floors if too loud.