My understanding is that this type of program is termed "fast-tracking" - One does 2 years IM, 2 years of research and then 2 clinical years in their chosen sub-specialty. From what I have been able to gather, these programs are generally filled by MD/PhD's or other people who have a significant amount of research - They are great programs if you can get them and, indeed, one can get NIH funding during the 2 years of research (35K/year) to help pay off medical school debt, thus mitigating some of the financial burden faced when going into academic medicine.
Best of luck for those of you who go this way!
Airborne
PS - do a search on "fast-tracking" to review the many previous threads in this area.