Building a $950 Diablo III PC: Confront Evil’s Rebirth on a Budget
Let's think about this for a minute. You're not building a Blackintosh, so OS X is out. You want to play games, so Linux is out. I wonder which OS we're going to install?
There's no denying that Windows 7 is the greatest thing out of Redmond. It's fast, fluid, easy to use, and does pretty much everything. It's also your last chance to get on board before Windows goes all Metro with Windows 8. You most likely don't need anything in the professional version, so opt for Home Premium and save a few bucks.