It's all well and good that water can hold a lot more heat energy than air, but you have to remember that the water is going to be cooled by air too, and a chain is only as strong as it's weakest link, so they say. Same goes for water cooling kits, so invest in a really good radiator, preferably one big enough to take 2 or 3 12cm fans, and quiet fans for that matter, or it's a pointless affair if noise reduction is your goal.
What's the chipset and CPU you are cooling though? a decent HSF is sometimes more efficient and does a better job than some medium range water cooling kits, such as a £12 Arctic Cooler Freezer 7 Pro, and if your chipset is performing at the FSB you want it to, why change? as the cooling solutions on them seldom make a lot of noise.
Look at my specs, I spent a good £55 on high performance, low noise air cooling equipment, and it's silent at those clockspeeds. So have a price up for high spec air components too just for info.
I'm not meaning to sound as if I'm putting you off, I just want to make sure you weigh up all the benifits against the costs and possible future complications. Water cooling is better when setup with the right, but expensive, gear. But if it's only for the "brag" factor, and minimal performance increase, it would be wise to take cost into account.
All the best!