depends on the school you go to. If the schools curriculum is designed for you to take it after 2nd year, then (from what I was told by some schools) thats how you do it.
For example: When I interviewed at buffalo, I asked them this very question. Buffalo is a traditional part-1 after 2nd year school.... they told me that a student who has not completed the classes covered in part 1 is not allowed to take the test, so simply finishing up first year there isn't enough.