From what I've heard, it's not the case itself that makes noise, but the fans. Ergo, if you want a quiet pc, just buy quiet fans. Recently, when I did a build of my own, I chose really cheap fans from deepcool, they were something like 5 dollars for each and they were supposed to be "ultra-quiet", however once my case accommodated six of them (each rated at 20 db) the pc became quite noisy. What would I Change if I was building the PC now? I would have bought only 3 fans, but they would have been more expensive and quieter. Take a look at Noctua. IMO their fans are overpriced, but performance and looks wise - they are astonishing. Bottom line is simply think how much fans do you really need and read reviews and roundups, like this one:http://www.bit-tech.net/hardware/cooling/2009/09/28/what-s-the-best-case-fan/6
Oh, and if you won't be gaming, then one or two fans OMO will be just enough.
Good luck with your build