As a business specialist, let me be completely honest.
Buy either an iMac run Bootcamp and load XP/Vista/7 if you don't want to have to keep wondering if that crash was because of hardware. If someone in the office (or knows someone) who is doing tertiary study, you can buy with an education discount which brings it in line with PC prices.
or
Buy a Dell Optiplex with 3 year NBD warranty for pure reliability. I have sold thousands of Dells from Vostro shitboxes through to some high end storage servers, and the number of issues I see compared to when I built whiteboxes is pehnomenal. 1 of every 10 or so whiteboxes would have at least one minor hardware issue (RAM/DVD/HDD etc) which is simple to fix, while one in every 50 or so would have a major recurring issue much harder to find. Of the Dells I have sold (perhaps 4000 or so) I have had only one issue that Dell had to replace the whole PC for (to keep cost of repair down) and perhaps 10 or so issues where a hard drive failed or ram failed.
Building an AMD for an office PC is a fucking retarded move all round.