Personally, I would't be caught dead building my own server computers in 2010. The pricing from name-brand vendors, with support and warranty, is very, very good and you're not going to mysterious compatibility issues (issues with boards not fitting in cases, power supplies not having enough "oomph", devices not fitting into slots, RAM not working on a board, etc).
Assuming you don't go crazy with the initial specs, the Dell PowerEdge T310 will do what you're looking for under $1,000.00. You only get a single processor socket, but you can put quad-core Xeon processors in it. It has a maximum memory capacity of 32GB and supports a pretty nice variety of processor, RAID controller, and hard disk drive options (and, of course, you can get multi-year warranty and support contracts).
Equipped with a single Xeon X3440 processor (2.53 GHz, 8M Cache, Turbo, HT), 8GB of RAM, a single 500GB SATA hard disk drive, and a 3 year next-business day warranty Dell will sell you the box, right now, for $899.00. You can add another hard disk drive to fulfill your 2nd disk requirement.
I don't mean to sound like a shill for Dell. I use their gear in a lot of Customer sites and I'm very happy with the gear and Dell's support.