Network storage and media system

Hi,

I want to build a home system with two main purposes: reliable and centralized data storage, and audio/video reproduction. No TV or radio for now, just CDs, music from hard drive, and DVDs. No need to run latest games on highest settings. Maybe I'd like to use a remote-control, although that's quite low priority. For now I have a regular flat-panel monitor, no fancy TVs or anything. That may change later. I will want to use it as NAS.

I am imagining a system where I will eventually store all my music, lots of personal documents, and maybe movies. I also want considerable extensibility, in case I wish to use it for other purposes in the future.

I am mainly considering a Linux-based system, since I am most comfortable with administration of Linux. Probably Ubuntu is a good choice.

Now, I have never in my life built a system from scratch, so I am kinda baffled by the too many choices and acronyms. From newegg, for $850 I can get:
2GB ram
1 - 1.5 TB disk, depending on the kind of RAID that I use
2.something GHz dual core Athlon CPU

The specifics are below, and I will appreciate any advice. Are some components overkill, is some money wasted? Have you had similar requirements and found something particularly useful or necessary? Did I choose some poor component? Do some components clash? Do some work poorly with Linux? Can you suggest alternatives? Lots of questions

Thanks in advance for any help!

- mobo:
$50 ASUS M2N-MX SE Plus AM2+/AM2 NVIDIA GeForce 6100 Micro ATX AMD Motherboard
or
$50 ASRock ALiveNF6P-VSTA AM2+/AM2 NVIDIA GeForce 6150SE / nForce 430 Micro ATX AMD Motherboard
(don't know how to decide)

- case:
$120 SILVERSTONE Black Aluminum front panel, 0.8 mm SECC body SST-LC17-B ATX Media Center / HTPC Case - Retail
(looks like a stereo component -- it'd stack nicely under my amplifier)

- CPU:
$90 AMD Athlon X2 4850e 2.5GHz Socket AM2 45W Dual-Core Processor Model ADH4850DOBOX

- memory:
$60 Kingston HyperX 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit

- HDDs:
$320 4 x Western Digital Caviar SE WD5000AAJS 500GB 7200 RPM SATA 3.0Gb/s
(i'd like to do software RAID, probably 1 or 5)

- power:
$110 PC Power & Cooling S610EPS 610W Continuous @ 40°C EPS12V

- audio:
$100 M-AUDIO Audiophile 2496 PCI Interface 4-In-4-Out Audio Card with MIDI and Digital I-O
(i want good quality output, as this will be my primary audio source)

Well thanks for the swift reply!

Frankly, I chose micro ATX boards because I have no idea what I am doing I only know what I want. I didn't even notice they were micro ATX. My criteria for choosing were:
- < $100
- integrated NVidia graphics
- newegg says:

(I only care about "4 SATA devices", b/c I want to set up RAID; however, I don't know if fewer "SATA devices" would be enough with port multipliers; would they?)

Thanks again!

I will do my reading, and then it's sleepy time for me. Thanks!

Just checking -- any further recommendations?