The home-made tool described at the bottom of this page has saved me a number of times when it came to removing stubborn French BB fixed cups:
http://www.sheldonbrown.com/tooltips/bbcups.html
Remember that if it is a French threaded bottom bracket, it will be "normal" right hand threaded, which means it was probably installed VERY tight so it wouldn't loosen itself over time. Expect it to be a bear.
-Sam