JohnVM:
you post is interesting, and I think I know what you need the system for, since you mentioned finance, I am thinking you are probably trying to create a Terabyte worth of financial data? (equity, options, commodities time series data?)
if I am right on my assumption of what you want to do , I don't think the system is going to get you what you want.
1. It's I/O. The areca will get you 500MB/sec fully configured. If you were to query a 2TB database, that's 4000seconds, or about an hour. Won't do you any good
2. SQL isn't designed for large time series database. You should look for column based database..go google for them(there are commercial ones like kx.com but since you think 5000 is expensive, kx is another story.
3. 4GB of memory is a mismatch for the amount of data in the SQL server. For what you want to do, a dual dual core Opteron system on Socket F with 8GB-16GB ram is more of what you need, for NUMA memory bandwidth instead of 1066FSB bandwidth on the Xeons. Plus DDR is cheaper than FB-DIMM
4. It's actually better to look at this problem from a scale out(having a cluster of cheaper systems) perspective instead of scale up(having 1 system that's like 1500 cores). You should look into either splitting the table into smaller ones, or having a distributed file system(lustrefs and hadoop file system) spread over multiple cheaper systems will do you more good.
5. one more thought: I hope your Windows 2003 Enterprise x64 and SQL 2005 Exterprise are properly licensed

if so, those licenses could cost you more than the physical system. a lot of distributed computing problems are not exactly done in Windows environments. Look into linux based distributed file system and clustering technologies for free. I recommend CentOS(since Redhat Advanced Server and SUSE Enterprise are very expensive)
that's just what I think...keep in touch.
if you don't go with the distributed approach, and insist on 1 big server, I recommend the following system:
1.Dual dual core Opterons (find the cheapest ones you can find, you don't be CPU bound, and you are going dual socket purely for the dual integrated NUMA memory controller found on the opterons) , you can get 2 of them for $400
2. 8GB(8x1GB) of memory minimum, 16GB(8x2GB) if you can afford them. 400-500 bux
3.a dual socket mobo $300-400
4.the 12 Samsung drives $800
5. Areca is fine, but get a DDR dimm for its cache(as big as it supports), although for your application, I am thinking maybe getting dual 8 channel PCI-E Areca's and then software RAID the two RAID-5s might get you close to 1GB/sec IO. $1000
so yes, you are looking at a $5000 system.
the distributed way:
get 4 1U Tyan Barebones, stick some cheap dual core E2160s in them 2GB each node and since the 1U tyans come in 4 hot swappable bays(RAID5 software), you are looking at buying 16 samsung SATAs to fill them, but this way it's cheaper, you can pull this off for 3000. Each 1U would have dual GigE, giving you 8Gigabit peak bandwidth over ethernet, probably a little slower than having dual Arecas in a single system.
As for the case, Cooler Master stacker is decent for lots of drives. If you want 1 system, you are going to have to pay for the hotswappable SATA cases like
http://www.newegg.com/Product/...x?Item=N82E16811152048