I'm one of those consumers who shoots, edits, and watches HD.
I wouldn't go with a Quadra video card unless the software you're going to be using absolutely requires it. While NVIDIA is a must, for their CUDA platform, which nearly all accelerated software uses, the standard consumer cards are a quarter of the price, and have exactly the same performance.
I used Hitachi Ultrastars in my last machine, but am back to Seagate Barracuda drives in my current system. Nothing wrong with the Hatachi, but they're not really price competitive (both cost within a few dollars of each other), but the Seagates are much easier to find. Be aware that in a RAID0 config, if you lose one drive you lose
all the data in the array.
My build (which is a bit more expensive, but considerably more powerful) goes like this:
Supermicro Case, Powersupply and Motherboard (has on-board RAID 0,1,10 (5 with an unlocking button from SM)).
2x Six-Core AMD Opterons (if you can find them at a good price, otherwise 2x Quad-Core Opterons).
As much of this
Crucial RAM as you like (up to 64GB), installed 4 modules (8GB) at a time (2 in each CPU bank).
1-8x
Seagate Constellation if you can find/afford them,
Barracudas otherwise.
1-4x
NVIDIA GeForce GTX 295, 4 of them will probably get you better than real time compression of 1920x1080 H.264 video with CUDA accelerated software, so sprinkle them in to taste.
