10 years ago I built a box using MDF and glass for my computer, using noise dampening foam and watercooling, space for two motherboards. (I had a lot of problems with headaches - noise made it worse, and I wanted to game.)
It was upgraded this summer to a GTX 780 hydro copper, new motherboard (z97) and the latest i7 that fitted, M.2 disk and windows 8.1. The other motherboard is running my Linux server, XBMC and the RAID.
It's about as big as a small fridge (55x70x50cm) and it weights about 55kg (10 liters of water) (it has wheels), but the noise level is below 10dB(A) (@1m); the pump and the disks are the loudest. It's more silent than the cats' water fountain - and it's more silent than this laptop on idle (well, firefox is heating it up as usual).
It's not impossible. It just takes some effort. The expensive part of watercooling is the water blocks, which you need a new one or two for every upgrade since CPU and GPU changes shape. (This time I went for the hydro copper so I wouldn't have to do the GPU watercooling myself.) Building a case is fun and will allow you to buy nice tools, useful for any craft.
Later on Zalman came out with the Reserator, allowing people to cool any system passively and very quietly. Are they still around? That is, I hear, a rather good solution.