Learn more here http://en.wikipedia.org/wiki/Peristaltic_pump
How Peristaltic Pumps Work? Peristaltic pumps work by squeezing a tube like you might squeeze a tube of toothpaste - except in this case the tube is a 5-foot-long silicone hose, with as much "toothpaste" as can fit in your bucket. This squeezing action is called 'occlusion'. Usually, you get this squeezing force by pressing the tube against the wall of the housing with a roller. The number of rollers in a pump determines how much fluid gets pumped for each pulse, the more rollers, the more pulses per revolution, the less fluid per pulse. All things being equal you get less fluid per revolution with more rollers, but smoother output. More rollers can also reduce the hose life.
Why build your own? As mentioned previously, peristaltic pumps don't require special materials, but there's a serious dearth of manufacturers building for the home market. You can buy little peri pumps for lab use or giant ones for industrial use, but not much in between. So, if you need to pump some wort around, want to water cool your laptop or just want to make a pump you can take with you and power with a drill, then a peristaltic pump may be the answer.
Ready to have a go? Follow along and get pumped up! (har har)
Here's some info on my setup:
A 'tour' of the pump