There are no core modules as such. I've just finished my second year but in my first year we had to study one medieval module, one early modern and two late modern and then two other choices. Each category (medieval, early modern, late modern) has a number of choices.
Have a look
http://www.dur.ac.uk/History/ugrads/handbook/Handbookaug2004.htm That's the first year handbook from this year - hope it gives you some idea but be warned that modules will change as some lecturers go on/come back from research leave.
I think they send you the 2005/05 version when you get your grades and your place is confirmed and then you can make your choices - at least that's what happened to me.
I'm not sure I've helped but I hope I have!!
Good luck with the exams.