The only possible way to have 'zombies' is 4 a virus to surface that decays our brain but leaves the body intact. When the 'zombies' get hungry(it would be impossible to eat all of the time), they would eat any meat(not just human flesh), or maybe even plants.
I think zombies could become real but they wouldn't be a threat. Simply corpses stumbling around eating the flesh of people who aren't smart enough to walk stay away from the slow zombies.
Actually it is possible to create a zombie, however none have been made, becuse....well it would just be retarded to.
there is no way to bring back long dead people (sorry guys, no nazi zombies) But they did manage to bring a dead dog back to live some how. And just through simplie processes you oculd make a "zombie" How ever it would not be like what you see in resident evil.