Take a wheat berry and break it into pieces (preferably with a steel roller, but at home you can use a blender or a food mill)-- you've got cracked wheat.

Bulgur can be called cracked wheat, because it is indeed cracked, but the difference is this: bulgur has been pre-cooked (steamed) then dried before grinding, while cracked wheat is uncooked. You can use them interchangably in recipes, however, you'll have to allow more time for cracked wheat to cook.