yeah, that mp3 car site rools.
there is a kit they sell which guides you through ripping apart your home pc and hard-installing the HD and CPU in your boot to play just about whatever you want....DVDs, Mp3s etc.
I had/have a nerd mate who in year 12, was too povvo to buy a head unit, so he installed an AC/DC converter and ran his computer and a solid state amp (A/B class) with a dual battery in his boot. he had the computer cd-rom drive installed in the din slot in his dash mounted on spring dampers....
....he also restored a model A ford, so I shouldnt laugh, but I did.