My experience with watercooling.
It is simple to setup, easy to maintain, extremely quiet and entirely dependent on one little pump that will give you grief to no end.
The new 64b processors actually run a lot cooler than these old crusty ones. The problem you still have is vid cards...any other heaat stacking cards. PCI slot fans are abnoxiously loud. Vented duct fans can be good, but can be loud...not to mention the digeradoo sound they somethimes make.
Here's one solution I used a while back because I just couldn't be bothered.
Build your system however you like. Make sure you have all the cooling you need. Be it fan, liquid, duct...whatever. Leve the case open on all sides. Get a huge box fan, like a 21"er. Plant it on the floor right in front of the puter. You will never hear the sound of the computer coolers over that!
Sorry if this wasn't helpfull. I was really just typing to hear myself clack.