The biggest "specialties" that most interior design students will distinguish in the course of their education is between Residential and Contract/Commercial design. Every program is different, but I am not aware of any that specializes in only one of these areas.
There are also specialties, such as kitchen and bathroom design, textiles or colors, etc. - but there aren't majors in these fields, per se. Rather, they're just part of an overall program which interior design students may choose to study through required or elective classes.
The best preparation for a career in interior design is from a program accredited by the Foundation for Interior Design Education Research (FIDER). However, individuals with degrees in other areas (i.e. architecture, industrial design) have been able to sit for the NCIDQ exam and practice interior design.
Besides the programs listed above, some institutions offer non-credit programs or workshops. You may even be able to take courses on a non-matriculated basis. But in order to become a professional in the field of Interior Design, one has to pass the two-day exam given by NCIDQ. In most states, passing this exam is required in order to become licensed or certified. In some states you cannot even call yourself an interior designer unless you have passed the NCIDQ test. This is the direction the profession is moving and the importance of being state-certified is generally recognized.