The curricula of both schools are similar. State licensing agencies and most hospitals and residency programs recognize the degrees as equivalent. In other words, ostepathic doctors are legally and professionally equlivalent to allopathic doctors. The important difference between the two types of schools of training is that osteopathic medical schools take a holistic perspective on practice of medicine based on a belief in treating the "whole patient" (mind-body-spirit) and the primacy of the musculoskeletal system in human health and the utility of osteopathic manipulative treatment. DO's emphasize prevention, a historical distinction which is less relevant as all of medicine increasingly emphasizes prevention.
There are fewer DO programs than MD programs with about 20% of medical students entering DO programs each year. As compared with traditional medical school, osteopathic medical schools have a reputation for looking at the applicant, not just his or her statistics, and therefore likely to admit nontraditional applicants who are older, non-science majors, or seeking a second career. The average GPA and MCAT scores for incoming students are slightly lower in osteopathic programs, but the difference is rapidly falling. The average age of entering osteopathic students is about 26 years (vs. allopathic medical school's 24). Both require an undergraduate degree and basic science coursework before applying.
The main disadvantage of choosing osteopathic medicine is that that you may find yourself educating patients and colleagues about your degree and credentials (i.e., that a DO is the equivalent of an MD).