In either case, the trouble is that, while the heatsinks can radiate away a fair amount of the temperature, you really need a fan nearby sucking it away a little more quickly. That passively cooled 3D card will be beaming its heat over the motherboard, so you'll need a fan close by to whisk it away.
It is possible to slap an almighty passive cooler onto a lower-power processor – which you could always underclock if you're trying to build a near-silent PC for media centre use only – but you'll likely only end up with your case fans spinning harder to cope with the increased overall system temperature. If you only need a PC for everyday desktop work, you could pick up an Intel Atom or Via Eden ITX board – these teeny processors barely generate any heat, so their minute cooling blocks are entirely passive. Just don't expect to be watching a cavalcade of high def video on 'em.
Enjoy the Silence
For a truly silent PC, even watercooling won't do the trick – there'll always be the subtle gurgle of liquid trickling through all those tubes and the pump that makes it happen. What you want is no moving parts whatsoever. To do that, you need to defy what common sense is screaming at you and submerge your entire PC, sitting it inside a liquid bath, surrounded by so much juice that fans simply aren't necessary. Just so long as it's nonconductive liquid.
What you need is mineral oil, and lots of it – a few dozen pints of the stuff. Given it's commonly used as a laxative and as Vaseline, acquiring the stuff may be a little embarrassing, plus expensive. A top tip, apparently, is to speak to a friendly vet, as they keep the requisite gallons of it around to relieve the bowels of constipated horses. Delightful.
It's possible to use vegetable oil instead, but as anyone who doesn't clean their kitchen regularly will know, that stuff turns nasty after a while. Once you have your oil, you can build your PC inside a suitably-sized aquarium, fill 'er up and you're most of the way there. Two things to bear in mind: firstly, you'll need to make your system air-tight to prevent evaporation, unless you want to be topping it up on a regular basis.
Secondly, you won't be able to submerge the hard drive, due to the infamous tiny hole you're not supposed to cover. An external enclosure will pretty much silence it, or alternatively you pick up a solid state drive which can be safely sunk – there's a guide to the parts you'll need and how to do it at www.pugetsystems.com/submerged.php.
First published in PC Format, Issue 220