First thing I would do is get rid of the MS operating system. Switching to Linux can greatly increase reliability. And it's free in most cases. There are a lot of really good reasons that most major servers aren't running an OS from MS. Security and reliability are just the tip of the iceberg.

Second, a suspect that a simple RAID 0 array would be fine. Your not talking about an uber-gamer who needs to worry about split-second response. A few extra ms on a write cycle isn't much of a burden in this case.

Third, while there is a tendency to go to huge HDs if they aren't needed, in part because the site is held on a central server, your just wasting money. Unless you tend to store an extensive picture collection, or a somewhat less extensive video collection, most people can get along fine with a 250GB drive. Adjust up or down as seems reasonable. With the money saved you can buy a DVD writer and use them for backup. Make two copies and store one off site.

Smaller drives also promote replacing them every few years. Which gives you a lot of advantages. The cost per GB has fallen drastically and looks like it will continue to do so. When I started 250MB, not GB, was a weeks wage. Half a terabyte, 2000 times as much space, is now a similar price. Replacement and copying to a new drive is a good time to review contents and cull out the dead wood. It also means you get better reliability because you replace them before they can fail or fill. And replacing them every few years means you can take advantage of new technology, speed, reliability as they become available.