The idea behind WCG is to execute in a few months important research projects, as demanded by leading research institutions, that would take thousands of years to finish with the available computational resources in universities and research centers. Therefore, whenever someone decide to participate in such a project, this person will join the efforts of hundreds or maybe hundreds of thousands other users that have done the same, composing a huge network of computers (i.e., a grid) which provides the necessary processing power to do the hard job within the strict time constraints required by the urgent nature of the projects.
All of these is done without any interference in the way you use your PC. The only thing that is needed is to download the program which will be running on the background as a screensaver, only when you are not interacting with your desktop.
Some people complain they would like to help the world to be a better place but they don't know how, or worse, they don't have the necessary time. These must not serve as excuses anymore. Stand up now and help to change the world from your bedroom.
Learn how to help on: http://www.worldcommunitygrid.org