For computer parts: Pricewatch
For car power supply: Opus or ITPS (I don't know the URL, but try
As far as components, for just movies and mp3s, get 512mb RAM, at least more than 900 mhz processor, video can be onboard IF IT IS A STANDALONE CHIP. Don't use shared memory, you'll see your performance take a hit. 200 gigs is a lot...I have one, its filled with Anime and movies, but the best way to do movies is just burn them on a CD (or DVD if it's a copied DVD).