will corn grow in peet moss cups?

Yes, they'll grow just fine at first. I assume you're talking about either peat pots or peat pellets (http://tnfarmsupply.com/images/340.jpg and http://northwesteddy.com/perspectives/images/basil... respectively, for examples), both of which are great for starting many kinds of plants from seeds. For peat pots, fill the pot with soil and plant the seed about 1 1/2" deep; for peat pellets, water them until they expand (follow the directions on the package) and push the seed about 1/2" into the moist peat. Keep them watered and supplied with sunlight, etc. until they're about 6" tall, then transplant them into a garden outdoors or a much larger pot.

You will eventually need a bigger place to grow them. Although corn's root system isn't too deep, it needs space: keep in mind that these plants will top out at over 6' tall if allowed to mature fully!

yes they are good for germinating but not for growing to maturity, you will transplant them when they are about 6 inchesl