Why is this important? Well, first you have to know a bit about proteins. We are creatures made up of protein. In fact, proteins make up over 50% of the dry weight of humans. Proteins build and maintain cells and perform all sorts of vital tasks in the body, too... your entire immune system is made up of proteins, as is your digestive system, as is insulin, and hemoglobin, and basically a ton of things that basically make your life possible.
Medical science knows a lot about the various forms of protein and what they do... and it also knows a lot about DNA and how it forms the blueprint that makes us who we are. What modern science doesn't know much about is how protein self-assembles, or folds, to actually build what the blueprint has laid out. This is a damn important thing to know... especially when you consider all the problems that can happen to people when something goes wrong with the building process... things like cancer, Alzheimer's, cystic fibrosis, etc... things that kill people everyday.
The tricky thing is that although proteins themselves fold extremely rapidly, simulating how proteins fold is extremely complex and very hard to do without massive computing power. Fortunately, a problem like this is perfect for distributed computing. There are currently 6700 users running Folding@Home... but the project is so involved it could use thousands and thousands more users who are willing to let their computer do a bit of number crunching when they aren't using it themselves.
By solving the riddle of protein folding, scientists hope to be able to come up with treatments and possible cures for numerous diseases... as well as advancing the science of nanotechnology. Learning about how proteins fold will also teach us how to design protein-sized "nanomachines" to do similar tasks. Of course, before nanomachines can carry out any activity, they must also be assembled.
In short, there are a lot of good reasons to use Folding@Home as your screensaver. There are versions of the software for both Windows and Linux. More information is available at the Folding@Home website.
