Ok dok. One other useful FAQ is at
http://www.med.upenn.edu/mstp/applicantfaq.pdf
For the cirriculum, as RxnMan says, schools are typically set up as 2 years of MD, PhD, then 2 years of MD. That being said, there are a few little tricks like getting rid of med school elective time and doing grad school rotations early that saves you a year or two over doing the MD and PhD seperately. The PhD is a standard PhD: you take a year or two of coursework, do a few rotations, then slave away in a lab for a few years to get a thesis out before returning to medicine. In general, there is a little bit of crosstalk between the MD and PhD cirricula. For example, you can often take a graduate credit per semester while in your first two years of medical school, helping to speed up your PhD. Also, during your summers, you do graduate school rotations, and some even start doing this the summer before first year. In graduate school, there are often programs to help you keep thinking about medicine, but in general this is a small amount of your time and doesn't count for very much.
With your MD/PhD you can practice medicine OR research OR both. They are both, full, official degrees. 99% of students go on to do a residency.
It's hard for me to give an example course schedule, because there's just so many darn courses and so many per semester, but here's approximately what I've done. Some of this is specific to my school, but you'll get the idea I hope.
Summer before 1st year - grad school rotation
1st semester - anatomy, physiology, histology, genetics, biochemistry, and more. On top of that "Topics in Molecular Medicine" seminar in the late afternoon once a week which counts as a grad school elective credit.
2nd semester - organ blocks. Pathology, pharmacology, and physiology of the specific organ systems in blocks lasting about 1 or 2 weeks each. I took an advanced math course twice a week at night.
Summer between 1st and 2nd year - grad school rotation
3rd semester - more organ blocks, alot of clinics preparation
4th semester - My school starts clinics 6 months early, so I did medicine, family, neuro, and psychiatry rotations. (I'm really glad I got this before starting grad school btw!)
Summer between 2nd and 3rd year - USMLE Step 1, 6 weeks off (I went and studied in Guatemala)
5th semester - 4 graduate school courses and a rotation
6th semester - 4 more graduate school courses
Summer between 3rd and 4th year - Defended pre-liminary exam
Now: Working on thesis. Going for a combined total of 7 years (with a couple months off before returning to med school).
That all being said, it's not as bad as it looks! In general, I have worked anywhere from 30-60 hours/week depending on the week. I probably average around 40. I take about a month a year of vacation, and I have travelled to Greece, Vancouver, Honduras (x2), Mexico, and Guatemala since starting the program. Before starting the program I toured much of Western Europe.