As someone who was just accepted into the 5PW program (woo woo), I can echo what Stephen said. The AMA created the 5PW program in the early 1970's for American citizens and permanent residents who go to med school in a country whose government requires a year of internship and a year of social service (after 4 years of school) before they grant the MD degree. The Carib schools (Ross, SGU, etc.) grant the MD after 4 years of school and don't require the internship and social service.
Some benefits of doing 5 PW are that we bypass ECFMG certification (and don't have to take the TOEFL and CSA). We go through this year of "supervised clinical training" and then enter the Match as Independent Applicants. Note that in a couple of years (I think it starts with 2004's entering classes)
everyone will have to take the CSA (or some version of it).
Right now, NYMC is the only school in the country to offer the 5PW program. You can check out their website at:
http://www.nymc.edu/depthome/fifth.asp The CA state government has just passed a bill to re-implement 5PW's in that state, but there is still a lot of work to be done before any of the programs open (even though there were 4 schools in CA in the past who had programs). For example, they still have to identify schools who might want to administer the programs, develop the curricula, and the CA Medical Board (and, I assume, the AMA) must approve each of the programs before it opens. CA AB 2872 is the name of the bill/law. Sorry, I don't have the address on hand, but you can probably search here:
http://www.ca.gov/state/portal/myca_homepage.jsp to find it.
I'm about to enter my last semester as a UAG (Guadalajara) student. If you have any questions about UAG or 5PW, you can PM me.