I think that you should search the AAMC site first. Choose the schools that interest you. Search their website for more information. If they list a contact for the joint program, CALL THEM!
I can't remember, I think it was Cornell, that it wasn't till the interview I found out that for their joint MPH with Columbia, they select 2 students per year and that is it. I believe it was Cornell. Anyway, just call the office or the contact to make sure that if you attend their school, there isn't a complicated process to do the joint program. Also ask about funding. Some schools list a joint program, but it requires you take an extra year, and pay for it yourself. I know it is way early to think about this, but just ask as many questions as possible.
My favorite joint programs: Duke(4yrs, free MPH at UNC Chapel Hill and Emory, also 4 years). I loved Pitt for medical school, but their MPH is an extra year and you have to pay for it yourself (basically paying for 5 years of medical school).
Hope this helps