@Chris Hamilton
Just to add to the mix:
Ulster <> Northern Ireland.
The island of Ireland has 32 counties (26 in the Rep., 6 in NI).
Also contains 4 provinces. These 4 are Leinster, Connacht, Munster and Ulster. (Might recognise some rugby teams named after these!).
Ulster is made up of the 6 counties of NI - Fermanagh, Antrim, Tyrone, Down, Armagh + Derry/Londonderry (last one's name depending on who you are), *plus* 3 counties Donegal, Cavan and Monaghan from the Republic.
So to say Ulster meaning NI, while it is done, (e.g. "Ulster says No") isn't strictly correct.
Another aside:
If you want to further wonder about all this look at sports:
Soccer - national teams for England, Scotland, Wales, NI, ROI
Rugby - national teams for England, Scotland, Wales one team "Ireland" - which is ROI+NI
Athletics - Team GB (England, Scotland, Wales + NI - should probably be called Team UK) and Team Ireland (ROI only)
Why all the differences??