I am in a similar situation as BladeRunner. My water is chilled to 10-15C by copper pipe in the ground. I get condensation on my blocks if its very humid and I then cook something like soup that adds a lot of moisture to the air (my kitchen/living room is one large room and my computer is there). When this occurs I've been avoiding condensation by opening some windows to vent the steam and cool the room down.
This chimney idea is very interesting to me. Its now one of the solutions that I may try out. I also like the idea of cooling a sealed case with a radiator and fan.
I have been considering raising the temp of my water to ambient by using a valve that would recirculate a portion of the water back through my blocks before it goes through my underground radiator. But its hard to give up the cold water.
Edit: After reading about surlyjoe's project at
AOA Forums I'm going with the radiator and fan idea. He put a heater core in front of his intake fan in the lower front of the case. His chilled water passes through that first on the way to the blocks. But I'm going to put the rad after my gpu block for slightly lower block temps and easier plumbing for my particular set up.