Getting a good residency has a lot to do with doing a rotation through the program you want to get into. You gotta prove to them that you'd fit in nicely at their program. This, of course, is easier said than done because there are often other just as motivated and talented candidates as yourself. The fact that you are a DO will be pretty irrelevant. However, there are some MD programs that are notorious for not taking DO's. Orthopaedics, for example, is extremely competitive among MD's alone, and they won't even look at a DO unless you are something beyond extrordinary, although there may be a few exceptions to this rule that I'm unaware of. The problem is compouned by that fact that there are very few DO ortho programs, so the competition continues.