Yeah man. Just like me you have the wrong impression of water coolings abilities. The top air solutions with the best copper heatsinks and vantec tornados come awfully close to that of top knotch water cooling setups and top knotch water cooling = deep pockets.
Like ender said you'd be talking about using peltiers which are in TEC (thermoelectric) cooling units and those require their own power supply, and depending on the wattage of the peltier protection against condensation.
So if you aren't willing to throw down a nice chunk of cash, then I wouldn't expect temps cooler than what you currently have on the CPU anyway...the GPU would definitely be cooled by even a decent water cooling kit.