[header] How to build a fileserver [title] Think about your needs. [step] Do you have to server hundreds of movies to multiple independent pcs throughout a house, or do you just need a convenient place to put your music to play on your htpc? The use of a home fileserver will strongly guide the next steps. [title] Think about storage space. 
[step] How much do you need? This is also tied closely to the last question. If all you have is a couple hd movies (or many dvd-quality movies) and a bit of music, you could probably get away with a single 500 gb drive.