Well, IT is primarily an applicative branch, it deals with solving problems with existing software. Whereas CS is a developmental branch - you create new software. But that's a very crude way to put it, as such CS has much wider scope than IT.
IT and CS are totally different fields. Careers are different. CS graduates hardly replace IT Graduates. CS takes focus in scientific research, scientific programming, and software engineering where IT in information system and information management. Some parts are overlapping each other. Both the courses offer different degrees. B.Tech Computer science focuses on intensive programming, mathematical skills and developing of new technologies and concepts. Bachelor of Computer Application focuses more on practical applications and technologies used in daily life. An Engineering degree is more of developing concepts and testing them, whereas Bachelor of Computer application is the study of putting these concepts to daily use. CSE = hardware + software IT= software only