I water-cooled my old 1.3GHz Athlon. Had a fish-tank pump in a tupperware running water and antifreezer through a water-block on the CPU up to a heater core off an old toyota that was mounted in the top of the case. Even rigged up a relay into a 120V receptacle so the pump would kick on whenever the PC was on. Ran great for years until the tubing started to get brittle and lose its elasticity; every time I jostled the tubing to much with my hard drives or add another stick of RAM, a minute amount of coolant would seep out and drip into my graphics card. There was never a trace, and never a drop any time I looked. Destroyed 3 cards before I discovered what was going on.
The temperatures I got weren't even all that great. But I had a lot of fun tinkering with it, which is was the real reason I did it in the first place.
After the fiasco with the leaks, I switched to passive evaporative phase change (heat pipe) when I build my 3.2GHz P4 box.
