No, never put them together. For a lot of reasons.
Your betta will go after other fish with bright colors, that's why most people keep dull colored fish with short fins with their betta. But even a dull colored Paradise fish would be a problem. They grow 2 to 3 times the size of a betta and betta and Paradise fish are both predators. With the paradise fish being larger, your betta is lunch.
They're from the same family, yes, and share the prefrence for a solitary life. If you want to get a Paradise fish, keep it alone or with bottom feeder of your choice, but never another betta. They'll fight, the same if you had two bettas in a tank together.
Last edited by MollyJean; 01-11-2010 at 09:27 PM.