Hi Tarquin,
Why not measure the width and length of window area that you want to put curtains on, then ring Duffys, Earl Street, Hickeys Fabrics, Henry Street, or Hickeys Home Focus, Blanchardstown. I always find these shops useful. If you give the measurements they will tell you how much you require for each window and they will give you a price, dependent on the kind you need, patterened or plain, etc. I hope I'm not stating the obvious but sometimes it just doesn't occur to me to ring around before I start out. As the ad says let your fingers do the walking.
Cheers