Start here to see Beck testimonials: http://www.dragonfly75.com/eng/stories.html
If you go to the Rife forum you'll see posts about the theory and different frequencies but no great testimonies. The most anyone says is it "helped me" like all the Clark Zapper devices which only have a slight stimulatory effect on the immune system. Oh also you'll see people trying to sell their Rife device (because it isn't effective).
Beck summed it all up when he said "Rife and Clark devices don't work".