I have just installed a new HDD in one of these for a friend of mine. A 500GB Western Digital I bought from ebuyer.com for £60.00. But try what Chris Green suggests just in case you don't need one.
Could you load music onto a SD card and then hook it up to your hi-fi system as a music player? Using the 3.5mm jack plug as the output with RCA connections to your amplifier. This is what I do with my iPod and iPhone.