You should have a thermometer in your hedgehog's cage at all times so you can monitor the temperature. It should always be between 72*F and 82*F. 100 degrees is much too high. Hedgehogs will start going through estivation, which is much like hibernation but is instead caused by being too hot. Some will do this as low as 82* so you have to be careful.
Signs of being too hot include "splatting" on the belly and panting. Estivation will bring sluggishness and lethargy.
You need to buy a good digital thermometer to ensure that your hedgehog is at the right temperature at all times. This is essential to good health.
This post has information about emergency cooling at the bottom: viewtopic.php?f=8&t=94&p=351
. It's much the same as what Shelby's mom described.
The floor is also a cooler place, so if you have a two story house on the floor on the first floor will be the coolest spot.
Those are really only temporary solutions though so you should try to find a more permanent way to keep the hedgie's room cool during the summer.