That box above will support dual core as well. So, for about $100-125 more you should be able to get a decent dual core chip. The mini-itx boards that would meet your needs are in the $250 range where the comparable standard size boards with the same functionality run in the $50-$75 range, so you are definitely paying for the small size. It's one of those things where you can build it good enough to get by but for only a little more you can build a full blown system that will handle anything you'll throw at it. I
If you are going for the full blown system then I'd stick with a standard form factor machine that you can stick in additional drives as you upgrade down the road. The reduction in main board cost could then allocate money to extra ram, faster processor, or even an extra quite case.
The last decision would be the OS. Windows is easy, but expensive, and Linux/Unix is more efficient, bu there's a learning curve.
