By Federal and Massachusetts law, all Harvard dorms, lecture halls, dining halls etc must be accessible to disabled students. See: http://aeo.fas.harvard.edu/freshmen.html
That said, Harvard only guarantees housing for FULL-TiME students, regardless of disabilities. If you are planning on attending Harvard part time (defined as taking fewer than 4 classes per semester), you need to find housing on your own. See: http://static.fas.harvard.edu/registrar/ugrad_handbook/current/chapter2/registration_course_enrollment.html