If you are trying to build a really quiet pc, I would avoid smaller cases. The cramped spaces tend to cause things to get hot inside, and thus your fans will have to blow more air to keep things cool (making things noisier). A bigger case has more room for the heat to radiate.
You'd be surprised. In this case, the cooling is designed to match and surpass (as in lower) noise levels of normal mATX and ATX enclosures. The term to look for is "Intel Mt. Jade Reference Design", there are multiple case manufacturers that offer enclosures that include this technology. Fi. All BK and BL (low profile cards only) series of Inwin use this technology, as do some Enlight designs and I know there are already some others. The real beauty is that it's using the Intel box cooler (i.e. cheap), which is then driven at lower rpms than I've ever seen before. It's the first cooling solution of Intel that actually works, and looking at the whole package it is REALLY cheap: for the price of just an Antec enclosure you can get a SFF enclosure, with better acoustics and a pretty good 80+ power supply. Plus you don't need an expensive after market cooler for your CPU. But please beware your board needs to fit within the Intel mATX guidelines for it's layout. The Intel mITX like the D945GCLF doesn't fit, even though it's smaller than mATX. And you can't fit big videocards in such a small enclosure of course (though a passive 8500GT is no problem).