[edit] Steps

Put the Peep(s) on a plate.
Open the microwave door.
Put the plate in the microwave.
Close the door.
Set the time to how long you want it to. Thirty seconds to a minute should work nicely. (The peeps will deflate after removing.)
Press start.
Watch the peep(s).
Press stop and open the door.
After.

Look at the peep(s) now!

[edit] Tips

Eat with a fork if you want to be a slave to the Peeps. (see below)
Get some graham crackers and some Easter chocolate (those foil-wrapped chocolate eggs are good for this) for a colorful Easter S'more. (but just for decoration. See below.)
Despite rumors to the contrary, exploding a Peep in the microwave does not occur as quickly as it would appear. If you truly want a sticky gooey mess and the explosion, then don't take them out of the original box and leave on the plastic wrap. Set the time on the microwave for about five minutes, and then, well, boom. You can use the link below to see a pic of the results if you'd rather not clean up a microwave afterwards.
Do this to as many Peeps as possible to stop them from taking over the world!
Remember to throw it away to prevent yourself from becoming a slave to the Peeps!
Something extra fun to do is to stick a toothpick in each Peep, then put the Peeps close to each other so the toothpicks barely touch. Put them in the microwave, then watch the "battle."

Don't hurt yourself; it is recommended to eat with a fork.(you will be a slave to the Peeps if you eat it at all.)
Make sure you use a large enough plate. The peeps will expand to the size of a softball when microwaved.
If you leave them in the microwave too long, they may 'pop' and make a big, sticky mess.
It will be really sticky.