You might want to look at the WHS (windows home server) option. I have been using one of my spare computers loaded with WHS V1 for about 4 years and it never has a drop of trouble. Currently WHS 2011 is available too, but it no longer has a much needed tool called “drive extender” which allows the WHS V1 systems to add hard drives. With WHS 2011 you need an additional third party drive extender, making WHS a less attractive alternative.
Companies that sell NAS charge a lot more then you would spend setting up a simple WHS. And, if you can find the old WHS V1 software, you can add hard drives up to the max your motherboard can handle. I currently run 6TB, but can add two more 2TB drives bringing my system to its 10TB max. Each drive is 2TB (the max size for each drive with WHS V1).
Long story short … The Western Digital WD AV-GP WD20EURS 2TB 64MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive is currently $109.00 from Newegg.com and is a rock solid full time (24x7x365) audio video server HDU (in case you intend to leave it running constantly).
Just one idea. Have FUN with whatever you set up.