Just a little input on the actual fluid used for the system. While ordinary car engine coolant will sufffice I did a great amount of research of the viscosity and thermal properties of fluids prior to setting my rig up. While antifreeze is a good additive at higher temps such as a cars engine its cooling capacities at lower temps is not as good as other alternatives. The viscosity of the ehtylene glycol solution leads to less flow in an arena where flow is the name of the game and also the thermal properties retain the heat longer. The best alternative That I have found is a mixture of reverse osmosis distilled water with a 70/30 mix of ethanol. I would not recommened using deionized water as it will turn your copper blocks into an cathode and cause it to corrode unless unless you are going to use cathodic protection and induce a positive charge on all you copper parts. Stainless is about the only metal that will hold up to constant exposure to deionized water. Ethanol has excellent thermal and viscous properties and also acts as an antimicrobal agent. It allows for even more temperature extremes if your are planning on super cooling your system and getting the coolant temps below zero with out adding to viscosity as glycol does as the temperature drops. And it is actually a cheaper alternative as it can be purchased already pre mixed in the form of windshield washing fluid made for freezing temps often less than a buck a gallon. Just read the label to make sure you are gettin the right stuff that does not foam and uses ethanol or ether alcohol.

I have been running water cooled for about 2 years now. I have a Koolance case with the water pump and radiator built in. It ran $400 when I got it but they are about $225 now, maybe less. Then you have to buy the processor , hard drive, and video card attachments separately. The system comes with the coolant and all the tubing you need. I got it mainly for heat, not to overclock. Other computer kept shutting down because it was getting too hot. Usually it averages about 84 degrees and is VERY stable. Haven't had any problems with leaks or anything. Only problem I had was my motherboard has to have a CPU fan or something connected to that power plug or it won't boot. If you do go this route, it's a good investment and you won't go wrong.

i use 80:20 water:antifreeze. Its widely regarded as one of the best mixes to use. I know guys that have experimented with several mixes and found this to be the best thing for low price. If I was made of money I would certainly be using something like 3M Fluorinert pf5060

3M Fluorinert pf5060 ACtually would stink for cooling IMO, I have seen this used a few times on some test setups but there were no blocks used at all. The entire assembly of the motherboard and it components were submerged in this elixir with 5/8" hoses running to and from the chamber they are submersed in. This stuff is very expensive and has unsrupassed dielectric properties.

That water cooling system is freakin a man !!! I want one. I read about different cooling systems in http://www.maximumpc.com they had some systems running almost at zero. If i can Ill post some links to different cooling systems. There alittle $$$$ though.

look for "phase change cooling" thats the real extreme of cooling for PC's. There are a couple of systems commercially available for home users, the Prometia and Vapochill (there may be others too) also if you have a little knowledge and time you can make ur own using a chiller unit and some other bits and bobs. These get temps down well below zero even at full load sometimes.