Follow LandShark's link to set up SETI.
But what I think you wanted was some background on the project itself. SETI @ Home is a distributed computing project that is searching for intelligent life out side of our own solar system. It is a privately funded project in which radio signals are recieved throught the worlds largest radio telescope, Arecibo in Puerto Rico, its the one that was in the James Bond film and Contact. See, all of the data that is recieved would take a very costly supercomputer, Cray's for example, and in order to save the millions of dollars a Cray is worth the data is split up into little Work Units (WUs) and you download these tiny 340Kb files and let your computer crunch on them for a couple hours. The program searches for all sorts of signals through a very advanced signal processing algorythm. And then you send the processed data back to Berkley, the university running the project.
Folding is pretty much the same thing, but instead of radio signals, you are crunching protein strands searching for a cure for cancer and other sorts of good-for-humanity things. I dont really know that much about folding so if anyone can better answer that one feel free to.
Either way you go these are great projects! Just have fun with it!