Scott is certainly right about the complexities of the science of tempering! But it can be fairly easily done. Marmalady has provided Jacques Torres' (my hero!) method, that I have never tried. Instead, my method is the old fashioned one.... But I firmly, firmly believe that measuring the temperature of the chocolate along the way is absolutely critical to tempering. Otherwise, you're just guessing...and that won't produce optimal results.
And if you're afraid of water or vapor from steam getting into the chocolate (water droplets caused by violent boiling in the bottom of a double boiler are much more likely than steam), then simply use a larger-walled bowl for the top of the double-boiler and place a tea towel between the bottom pan and the bowl...just be sure the towel cannot be touched and ignited by flames. My cooktop is ceramic, so it's a lot safer and the dripping water, if any, is not a concern either.
I've truly never had a failure using this method, but know that I take my dear sweet time in doing it:
Chop chocolate blocks into small pieces by chunking with a knife.
Fill bottom of double boiler so the hot water does not touch the bottom of the upper pan (I use a pyrex bowl for the upper pan). Do not let the water boil in the bottom of the boiler, but SIMMER! Stir the chocolate while melting to ensure even heating. Try to avoid creating air bubbles. Heat chocolate to 120 F. to 122 F.
Replace the hot water in the bottom of the boiler with 70 F. water, no cooler. Stir until the chocolate cools to between 79 F. and 80 F. It may occasionally be necessary to add additional cool water to the bottom of the double boiler.
Now replace the 70 F. water with warm water (about 92 F. to 93 F.) and raise the temperature of the chocolate to between 88 F. and 89 F. for dark chocolate or 84 F. to 86 F. for milk chocolate or white cocoa butter coating (white chocolate). Maintain the appropriate temperature while dipping. If the chocolate exceeds 90 F., it will be necessary to repeat the tempering process.
Yeah, on second thought, Marmalady's posting sure seem a lot easier!!! I guess I always seem to opt for the hard road not because I must, but because I can. My own personal therapy....!
Good luck, kyles!!! (Whatcha making?)