[dba-Tech] Building a network storage device

I have a need for a large, fast, redundant network storage array.  I need a
gigabit network link, raid redundancy, and terabyte capacity with the
ability to easily upgrade the capacity as my needs grow.  When I say fast,
this is intended to be a backup system, not a database or web server.  I
just need to be able to stream tens of gigabytes out to the storage for
backing up my SQL Server databases.  The backups will be compressed but will
still be anywhere from 10 - 40 or 50 gbytes.
 
Let me say up front that so far, all of the "NAS" solutions I've looked at
underwhelm me.  Many and perhaps most use 10/100 NICs, and a single large
drive, or perhaps a pair in raid1 configuration.  Wonderful for something
like personal computer backup but underpowered for my needs.
 
I have a spare computer with a "3 GHz" Athlon X64 processor, a gigabyte of
ram and a built in gigabit NIC.  It certainly seems like a raid 5 (or
preferably raid 6) array shared at the root level would serve admirably.
Throw a software firewall on it which filters to only allow local 192.xxx
address ranges to address it.  My network system is (ATM) WFW based and so I
would likely just stay with Windows XP as the OS.  
 
What I don't have is the raid array.  My experience with the built-in
motherboard raid controllers is that they pretty much suck so I am looking
to do an add-in card kind of thing.  I am looking at a pair of 750g drives
raid 5 which starts me out at 750g capacity, then simply adding additional
750g drives would add that much storage at a whack.  The 750g drives are
currently on the expensive end on a $/gb basis for the drives, but when the
system is taken as a whole the equation changes, plus it allows a large
capacity out in the future.  The price of these drives will no doubt drop
over the next year or two so the price would be more reasonable by the time
I need to expand.  Being able to go raid 6 at some point would be nice but
probably not critical.
 
I would like to know that if the system motherboard dies, I can yank the
controller and drives and place them in another system and be back in
business in short order.  Likewise if the raid controller dies, I could pop
in a spare controller and be back in business in short order.  
 
Any thoughts from you folks on this idea?  Has anyone done this.  Words of
wisdom?  Unless there is a compelling reason to do this, please leave out
the "go Linux" stuff.  I have enough to do without doing the star trek
thing.
 
John W. Colby
Colby Consulting
www.ColbyConsulting.com