Watercooling
can be quiet...just like aircooling. How quiet depends on several factors.
A typical WC setup just has the CPU being cooled. More advanced setups add another block for the videocard. The radiator usually has a 120mm fan on it. This is not as silent as people think.
Plus, you still need case fans to cool the HDs, mobo and memory; not to mention the PSU.
Most people that go to WC are hard-core enthusiasts looking to squeeze that last 5MHz out of their already smoking processor. :evil: and could care less about noise. A handful like yourself go after a silent PC. In the past, due to smaller CPU heatsinks, smaller 60mm fans had to be used. Any high performance 60mm fan is a 6,000rpm screamer. Newer heatsinks like the AX-7, SK-7, SLK800 to name a few, can take 80 and 92mm fans. Bigger fan = same CFM as little fan at a lot less rpm. I.E. quiet.
Before trying watercooling, try this. Order enough Panaflo L1A or Vantec Stealth fans to replace all the case fans in your case. If you are using the stock CPU HSF, order an AX-7 HS (about $15 if you search) and put another L1A on there. At that point, your videocard will most probably be the loudest thing in your system.
Case fans make the most noise in a system, unless you're running a monster fan on your CPU like a Tornado or Delta.
I have an AX-7 on my OCed XP2100. I have an Antec BB Fan on there; 34CFM. You can't hear it outside the case.

If I wasn't running it at 1.775v, I'd have a L1A on there, but it runs a little warmer at that voltage, needing more CFM for cooling.
A new HSF and five L1As will set you back about $35-$40. You can't get into watercooling for any less than 3x that. Give it a shot. You will be surprised at the results.