Unfortunately I could get neither of these to work, probably because of my own ineptitude.
I couldn't get VLC to output from Spotify, this could be my own fault.
I also couldn't make Airplay play with OS X 10.3.9.
I did however find a messy workaround.
I am currently using Airfoil on my main Desktop to output Spotify and then am receiving it on Airfoil Speaker on my iPhone, which is in turn connected to my 10.3.9 iMacs audio input via a 3.5mm Jack.
You need to download an app called LineIn for 10.3 (http://www.rogueamoeba.com/legacy/) to play the sound from the input from the built in speakers.
To be fair it's not that messy it just requires you to have a device that can have Airfoil Speakers installed on it and have a 3.5mm Jack.