what's the difference between a computer science major and an IT major?

Computer science often focuses on programming (writing software for applications, drivers, databases, operating systems, etc). IT tends to focus on networking and infrastructure, and the things needed to keep a company functional.

I agree with what Malica said from a career perspective - but I want to add - if you're asking from an education point of view - that varies greatly. The only way to truly know is to look at the courses that make up each of the degrees. Computer science and IT can be very vague terms and they're often abused. If you're asking because you're not sure what degree to get - look at what the specific courses make up each degree.