If the murky depths of my memories of school is correct, the location of the period is dictated by whether or not it is part of the quote. So, if the quote should have a period at the end, it goes inside the quotation marks. If the quote does not include the period (e.g. you are quoting part of a sentence), but you are at the end of a sentence in your own prose, you put the period on the outside of the quotation marks.