I just picked up a round frame bike called a Jupiter Beat Super Bike and it has a MX5 Superbike motor on it. Can anyone shed a little light here? History? Value?

Do you have any photos? I saw one of these once and it did not seem like a particularly nice or valuable bike, but you never know.

Is it the one with the hexagonal tubing?

No, this one has a round frame

Photos would helpful. The bicycle itself is probably not special. The Jupiter Beat bikes were department store/toy store fare. The motor might be worth something, new ones cost something like $400 from what I can find online.