Not to sound out of place, but those specs are overkill for what they want. I would suggest a 4 year lifetime and buy the cheapest POS Compaq you can get your hands on, and add a second HD to it (or not).
This is the scary thing for computer makers these days, even the 400 dollar machines will be capable for "too long". Regardless, of what they want, do not pay over 600 dollars for it, as that is a major error in monetary judgement. The only people who pay premium or even sub premium for a PC are those who need major power now. Wait for a few years after and if they need it add a GFX card (an "older-by-then" card)
To justify my logic: I have a file server that is 8 years old and a "livingroom computer" (the entertainment center) that is 11 years old and both are fully capable machines. Each can handle even the most modern of video codecs. Both of these machines where "off the press" types, not home built.