If I use dry yeast, I rehydrate using these steps (for an 11g pack):
1) When you are about to start your boil, put 1 cup water (not distilled) in a Pyrex cup in the microwave. Boil it down to about 1/2 cup.
2) Cover the cup with a piece of sanitized foil (sprayed with Star-San). Set it aside to cool to about 90-100*F.
3) Once the water has cooled, sanitize the yeast packet and cut open with sanitized scissors.
4) Sprinkle it on the water, cover and let sit 15 minutes.
5) Stir well, cover, and let sit 5 more minutes.
6) Hopefully by now, you have your wort chilled (about 62-65*F for a typical ale) and ready for the yeast.
7) The yeast slurry needs to be "attemperated" before you pitch it in the wort. That means you have to add small amounts of the cooler wort into the yeast slurry, stir and let it sit a few minutes. You'll probably have to do this a few times to get it to within 10*F of the wort temperature. Once it's within 10*F, pitch away.