Easy fellas.. he or she is new on the forum. You'd be surprised how many people I've come across in public who have asked this.
OP, you can take the USMLE if you want to get into an ACGME residency, but as an osteopathic student you'll also have to take the COMLEX set of exams. From what I've heard you can apply for the ACGME residency programs, and if you're unsuccessful scramble for an osteopathic residency as their match occurs before the ACMGE match. Some people believe there's better training, whether that is true or not I haven't got a clue as we're no where near that stage of the game, but to me I think it boils down to location as to why some places are more desirable than others. Either way, you'll graduate from osteopathic medical school with a DO, as that's the degree which is granted, and in America has full and equal practicing rights and since 2003 (is that correct?) one of the accreditation boards (forget which one) considers both MD and DO equal.