Just wanted to add a couple of things.

I have an HTPC and store all my blu rays, dvds, photos, music on my Unraid Media Server. I have 10 x 2TB drives. I started with 2 drives and and old pc case. I just recently upgraded my case to something that can handle 15 drives. I just add drives as I needed them. You can mix and match sizes. Personally I found it to be the best all round HTPC Media Server.

The Unraid server can run on some really small requirements. Mine is running on a P4 2.8 cpu and 2GB of ram. I haven't had a single problem in 4yrs. The software for 3 drives is free. You can read about it here -
http://lime-technology.com/

You can also check out their forums
http://lime-technology.com/forum/index.php

For the HTPC you should check out AVS Forums Guide to Building an HTPC, loads of great advice!

http://www.avsforum.com/avs-vb/showthread.php?t=940972


Hope that helps!