First off, I hope your going to put a CPU in that thing! :-P  I would suggest a quad-core because it should help your render times (most editing software is at least dual core, and newer versions will certainly support more cores if they don't already).
You are going to need to get a XP Pro 64-bit to be able to address all that memory.
I would recomend you look into RAID cards.  If you RAID using the motherboard controller, you are almost always tied to that controller, so you can't easily move the raid to a different machine (and if your motherboard dies, you have to get the exact same motherboard as a replacement to access your raid).  This is probably going to cost you at least 300 for a decent one.  The nice thing about it, however, is that any quality raid card will accept 4-6 drives at a minimum so you can expand your RAID at a later time (newegg carries one card that can accept 24 drives... but I don't think you want to spend $1k on a RAID card :-P).
I don't know which editing software you use, but Avid requires an nVidia card and suggests their Quadro FX cards (workstation cards).  Workstation cards are designed to take render load, but I always thought it was more for things like 3D modeling (Maya or AutoCAD), so I don't know if this will actually help you.  Both nVidia and AMD have good offerings as far as video cards (both in the desktop "gaming" market and workstation market), so I'll let you decide which one is best for you.
Other than that, I highly suggest the Dell 2408WFP monitor.  It's a 24" 8-bit monitor so you are dealing with true 16.7 million colors (as opposed to a 6-bit monitor which can technically only do approx 262 thousand colors and using dithering techniques mimic 16.2 million colors).  All in all, it doesn't matter which size/brand you get, but I strongly suggest you get an 8-bit panel.  I suggest the Dell because I have it and love it and even the uncalibrated delta E is quite minimal. :)
Now, if your going to have that much resolution, you also might want to look into a laser mouse if you don't have one already.  These aren't the same as optical mice- they are more sensative so you will be able to move the mouse less to travel the same distance.  I use a Microsoft Sidewinder mouse and can be found on Ebay for about $25, but this is a "gaming" mouse, so you might want to look at a more "normal" mouse.
My last question, and also the most important- what power supply to you plan to use?  Without knowing your CPU and GPU choices, I would say you'll probably want at a very minimum a 650W and always a trusted brand (Seasonic, Silverstone, PC Power & Cooling, higher end Thermaltakes).  Let me know your CPU/GPU choice and I can help make sure you get the power you need.  Remember, you wouldn't buy a corvette and put regular gas in it, so don't run your computer on a crappy power supply! :)
Hope this helps, let me know if you have any questions.
