Tech Arkade has done a nice little write-up on liquid cooling your computer. Part of their intro:

Today we are going to be taking a look at the process of water cooling a computer. Before the year 2000 this was an elite modification only done by a few. Almost all of the parts were custom fabricated or taken from automotive scrap yards. With computer parts getting faster and hotter after that point, many companies decided to capitalize on that small market. A few companies began to make “hobbyist” water cooling components. These parts have continued to increase in quality, improving performance and making the process easier than ever before!