Want to contribute something meaningful to the world, but don't have any money or time? Consider SETI at Home. It's your chance to help find intelligent life in the universe. And the best part is, aside from installing the program, you do NOTHING! Your computer does the work, you get the credit.
Little green men not your thing? You can do Climate Prediction too. Or help search for spinning neutron stars. Or look for the largest Prime Numbers.
So why not turn over a part of your computer for scientific research? It will make you lose weight, make you teeth whiter and make you more attractive to the opposite sex (or the same sex if you prefer). Well not really, but it can make you feel really good about all the time your computer sits idle.