Quad core and 8 GB of RAM? Is this a media center or a F@H bot?
I'm looking at doing something similar for a lower-power consumption alternative to running my gaming machine 24/7 as a file server and was going to run one of those little ~$30 Sempron CPUs unlocked to a dual core and 4GB of RAM. Doesn't need a whole lot of power, my 1.83GHz C2D in my laptop can run just about anything I need it to, and the Sempron will be faster once unlocked and should still run on very little power.
I haven't checked hard drive prices in a while, have they gone down? There was some serious flooding in Taiwan which caused HDD prices to spike, the 1.5TB WD Black I bought for $120 was nearly $400 last I checked...