Well, I don't know anything about the postbacc program, per se, but I went to Mt Holyoke as an undergrad. Assuming the premed postbacc program works the same as the other Frances Perkins programs, I can tell you a bit about how it works.
The FPs took classes with the rest of the undergrads. Since MHC is a small school, the largest class I ever took (geology) had less than 30 students in it,so you have more than ample opportunity to get to know the professors and other students. They were in the process of constructing some new science buildings when I was there, so as far as I know the facilities are relatively new.
As far as I know, the premed program is not 'formal' in the same way that, say, Goucher or Brynn Mawr is. By which I mean, there is not a set program of study with 2 semesters of gen chem in the summer, and Bio/orgo/physics in the fall and spring. Instead, you'll have some flexibility of planning and scheduling your own program, but you'll be able to work with an advisor to do so.
I am positive that you'll get great one-on-one advising during your tenure. I'm also fairly certain that you'll get a committee letter for your application - in fact, the alumni center suggested that if I took my science courses at a university that did not offer that service, I could submit letters and transcripts to MHC instead and they would write it into a committee letter format.
It's a beautiful campus, the education is top-notch, and they foster a supportive learning environment. I loved my time there. If I'd still been living in MA when I decided to go to med school, it would have been one of my top choices for postbac just because my experience at MHC was uniformly positive.
I'm sorry I don't know anything more concrete about the premed postbac program. Good luck with whatever you decide!
