What is the difference between an F-1 visa and a J-1 visa?
Students in the F-1 visa category are pursuing a full course of study and are usually totally funded by personal or family funds (and scholarships).
J-1 students are financed, at least partially, by the US or home government or are a part of an exchange program. The J category (which also includes teachers, scholars, researchers, and specialists) may subject the participant to a two-year home country physical presence requirement.
There are also differences in work permission, administration, and insurance requirements. (Summarized from NAFSA Adviser's Manual 2007 Release)