There are MD/MBA programs at a number of schools with students enrolled in them. In general they add on one year to your MD degree, meaning that you basically lose a bunch a business electives, and a bunch of medical electives (since to graduate from the B-School they are counting your med school classes and vice versa as your electives).
Some things to consider:
What year you take your last MBA classes:
To gain the most options you probably want to graduate at the same time as your MBA cohort (meainng starting it between your M3 and M4 years). This will allow you access to on-campus recruiting at your business school, in the year before graduation if you decide to not seek a residency.
What your career plans are:
If you are definitely not going to do residency, then WHERE you get your MBA counts for a ton. Unlike medical school, the drop off in prestige and thus employability is significant after the top 10-15 schools. Those 6 figure salaries you always here about MBAs getting right out of school? Basically only the top schools students get those. Check out either the last Business Week rankings or the last USNews rankings to get a sense of where schools stack up. To be frank, if you ever think about "jumping ship" your MD will help you more than your MBA probably unless you go to a top MBA program.
If you are definitely staying in medicine, it probably doesn't matter where you get the education, finance is finance, marketing is marketing, as far as the basic information.
If you are unsure about your career plans, then perhaps you need to rethink the MBA. Try looking for this book on Amazon:
MD/MBA: Physicians on the New Frontier of Medical Management
by Arthur Lazarus (Editor)
It is published by the American College of Physician Executives and talks about a number of career tracks that doctors have used after getting their MBAs.
Good Luck on your decision