CalBee,
I'm currently doing a Master's in P&S at the Health Sciences campus (now called the "Medical Center"). As mentioned it's further uptown. The campus houses the med students, the School of Nursing, Mailman Public Health school, School of Dentistry, the Graduate School of Arts and Sciences (within P&S), the new Genome center (Computational Biology, Biomedical/Chemical Engineering), and they're building some new buildings (called the Audubon buildings) with state of the art labs.
All other schools (law, education, essentially everything else) is <i>currently</i> located on the Morningside Campus on 116th. However, President Bollinger is planning a new 3rd campus in between the two, slated in "Manhattanville", which is, to my knowledge, near 145th-ish area. Columbia already owns quite a bit of real estate in that area. They still haven't decided who's going to reside there, but they are earmarking it as a more integrative center. The Genome center, Biomedical Engineering, Biomedical Informatics all have ties in both medicine/hospital organization, as well as other disciplines.
Interesting times at Columbia now, and certainly lots of support from the big people there to improve the facilities (they're already pretty nice if you ask me).