[Relmz]

The CPU & RAM seems a little overkill to me.
You really don't need a setup that powerful to run a file server - like arkay said, the main consideration would be that the motherboard you've chosen has enough HDD controllers (which it does).
I would suggest cutting back on the CPU & RAM - I don't think a system with those specs would never be used to it's full potential as just a media server, and you'll save a bit of cash at the same time.

I'd have to agree with tyronne27 - FreeNAS would also be my recommendation.
I've just setup a FreeNAS box on a P3 1GHz with 192MB RAM and so far it's worked perfectly for streaming my videos, music and pictures across the network to my PC's and xbox.

I haven't had a huge amount of experience with Linux, but the setup of FreeNAS was quite easy, and there's plenty of guides available on the net.