Here's the easy way to temper chocolate in the microwave. Jacques Torres demonstrated this technique on Episode 501 of "Martha Bakes."
Place chocolate in a large microwaveable bowl. Microwave in 20-second intervals, stirring after each interval. Remove bowl from microwave when two-thirds of the chocolate is fully melted and one-third is still in pieces.
Using a rubber spatula, transfer all of the chocolate to a room-temperature bowl. Carefully, using an immersion blender fully submerged in the chocolate, blend the chocolate until smooth. Using a laser thermometer, check the temperature. If the temperature is less than 90 degrees, use a hair dryer to heat up the chocolate while stirring continuously. If the temperature is more than 90 degrees, continue to stir, adding more pistoles or chopped chocolate to cool it down. When the temperature is 90 degrees, it is tempered and ready to use. If there is any leftover tempered chocolate, it may be stored in a re-sealable plastic bag and reserved for another use.
Use European chocolates, with a higher cocoa butter content, and pistoles or callets for easier tempering.
Dark chocolate is the easiest chocolate to temper, so start there and work your way towards white and milk.
Make sure to fully submerge the immersion blender when blending the chocolate, so that you don't aerate the chocolate.