MBBS programs vary region to region.. some have basic scineces in the first three years, some have basic sciences in the first two years.. and some Indian/Pakistani programs teach it througout the first four years, e.g. I know that in one of the MBBS schools, Systemic Pathology was taught in the fourth year...
However most of the Carribean School Systems are M.D. programs in which the first two years are just hard core basic sciences and from what you have posted above you said you are in the Carribean School System.
You are basically looking to cover the following subjects:
anat, biochem, histology, embryology, microbiology, immunology, pharmacology, pathology, Beh Sci.
You apply for step 1 via ecfmg and then have to get your medical school to sign off that you have completed those subjects and can give step 1. Once thats done you can give the exam.. Regardless of which system you are in.. concentrate on pathology (as I have been advised by my fellow SDNers!

!!) alot and then physiology and pharmac other subjects as well.. basically the 3Ps
Search around for which books are best to read while you are in your medical school years AND MAKE SURE YOU READ THEM and make sure your pace matches with the speed your lectures aer going.. if you attack it early, you won't have to pay for it later...
those are my two cents!