Le Château de Matel was where we lived during the week of our course. Our room is the left window on the second floor (called the "first floor", or première étage, in France). We paid a 150 euro supplement (for the week) for this large corner room.
Note added August 2009: L'Ecole des Trois Ponts is no longer in the Château de Mâtel, where we stayed. It has moved to the Villa Beaulieu, in Riorges, Grand Roanne. For up-to-date information, see their web page.
Perhaps the different ways of numbering the floors of a building reflect linguistic differences. Every building level has a "floor", even the ground floor, so in English, it's the first. On the other hand, the French word étage is related to the English word "stage" - it's something that's BUILT UP (an étagère is a set of shelves). Thus the ground floor could not possibly be an étage - the French call it the rez-de-chaussée, literally "the level of the street".