Check out http://folding.stanford.edu - It allows you to download a program that will use your computer to run computations on protein folding and the results will be sent back to Stanford and compiled for use in medical research. Have been running it for about a week with no ill effects. I had this running on my PC a few years ago but that site moved and I never did get the new site (for whatever reason) until now. If you decide to try it I would suggest that you configure the CPU to run at about 50% (on the configuration page) otherwise it may hog resources when you don't want it to. I have run it at both 50% and 100% and it doesn't seem to affect the speed of the computations too much, but my PC doesn't slow down at all at 50%.

Let me know what you think.