This was definitely a movie, cause I remember seeing the ending credits and everything. The movie concerns a teen scientist, who has a sister or she’s his peer/neighbor, all I know is that there’s this guy who does Frankenstein like experiments and this girl finds his lab, in which he has a brain in tank he reanimated and can talk and is generally intelligent. Again the girl finds the brain and they talk and the brain and she fall in love. All the while the teen scientist hires this other teen to help him with his experiments. Soon the teen scientist finds out the girl has been sneaking into his lab and gets mad at her and hits her, in front of the brain. Soon the guy then kills his assistant and puts the reanimated brain into him and then he is killed by the brain in its new body. He then meets up with the girl and they run off together in his new body. Its like The Man with Two Brains meets Sweet Valley High. I think it was a direct to video movie that either aired a lot on the SciFi channel or Showtime or HBO.