The France Grids
Lambert I, II, III, IV maps
Map Datum - Select the datum you want to use for the map, the most likely would be "European 1950 (Mean France)". Even though the France Grids use "NTF France" for the IGN coordinates there is no need to choose this as the map datum as OziExplorer will automatically use the "NTF France" datum in its internal calculations but produce the positions in the selected map datum.
Grid Selection - In the Map Projection field select the France grid number you want to use, this should be the grid number the map uses for the +'s placed on the map as these are the points which will be used for the calibration.
Use the + marks printed on the map for calibration. The numbers for the +'s are shown on the edge of the map. You must add 000 to the IGN coordinates shown on the map edge to get the full Easting or Northing.
New Maps (Lambert 93)
The new maps are much easier to calibrate as they have a full grid in UTM "WGS 84" printed on them.
Select the Map datum as WGS 84
Select the Map Projection as UTM.
(Actually it may be more accurate to select the Map Projection as Lambert Conformal Conic and set the parameters as Latitude 1 = 44deg, Latitude 2 = 49deg and the Central Meridian as 3deg.). However it doesn't seem to make much difference to the calibration.
Calibrate the points using the UTM Grid on the map. You must add 000 to the UTM coordinates shown on the map edge to get the full Easting or Northing.
The France Grid is also shown on the maps as +'s so it is also possible to calibrate using the same method as the Lambert I, II, III, IV maps..