How does dried cilantro relate to fresh?
Coriander, the plant, is the one whose leaves are called cilantro in many regions - the Spanish name for the plant. Of course, in some regions, the leaves are called coriander (or coriander leaves) as well. Coriander, the spice, is indeed the dried fruit/seeds of the plant, commonly sold both whole and ground. The seeds have a very different flavor from the leaves.

As for dried cilantro, the leaves? They're going to be pretty much flavorless compared to fresh cilantro. Cilantro loses its aroma quickly when heated or dried. Obviously there's still something left, or you wouldn't be able to buy dried cilantro, but it's not going to be a striking addition to a dish. If you can get it fresh, it's worth it.