Testing for collisions between rotated objects

I’m writing a general physics engine and I’ve come across the problem I’ve always had with flash. So far all my hittests in my physics engine have been calculated by using x/y coordinates and the 2 objects dimensions. This has worked fine for the objects so far because they have been very square-ish and do not rotated. How ever now I am trying to detect if 2 rotated objects are hitting. How can I do this ? I would really like to avoid using any .hitTest() functions.