Water is quiet, so if thats what you want its the way to go. But its expensive and dual is more complex them many people start out with. Keep that in mind.
I'd check out Procooling's articles (there is one on SMP cooling) as well as my entries in this FAQ
http://www.kpod.co.uk/ars/ (water is at the bottom).
Sorry if thats general, but I'm going to sleep now.