I had several watercooling systems before. First I started with a home made stuff, back then it was quite good, could handle those power hungry 1.4 athlons, and AXP over 2.7-9ghz.
Then I switched to branded one. Had dangerden blocks, pump, radiator and stuff. Dont know the current prices, but if you want a quality system, that does work well, it can easily cost you around 150-200$ at least.
About the noise. Pumps can make noise, especially if they vibrate in the case. The fan can make noise on the radiator. Although my system only had a 12cm fan at 800rpm.
BUT, and theres the but. If you arent doing extreme overclocks, its just unnecessary. Expensive, and its usually a pain to maintain (rearranging pc, cutting tubes, cleaning the block,s tubes and all that stuff). I had them for over 4-5 years, never had any problems with it. No leaking or anything. So I can call myself a WC fan. Still, Id recommend good air cooling.
I have this one:
http://www.thermalright.de/Kue ... nk+++IFX-10+-+Bundle.html
And keeps a C2D @4.0 at 1.35 around 50 at load. So WC is just not neccessary, unless you do some hard oc, or just want it to look cool.