What is the diference between a regular Dodge Charger and an R/T?
Just the engine or what? And aren't Charger Daytonas and Superbird Roadrunners the same car?

The engine and the paint job.

Charger Daytonas use the Dodge Charger 500 as their base car and put the nose cone and wing on that while the Superbird uses the Roadrunner as the base with the same nose cone and wing. Besides that, it's mainly the paint and decals as well as the engine.

Go here and they'll answer all your questions:

http://www.dodgecharger.com/forum/index.php