I have a feeling that there has been a significant development which hasn't been revealed publicly yet. Perhaps we shared some intelligence with Paris regarding Saddam.
Or possibly it's just a recognition on their part that we are going into Baghdad regardless and they don't want to be left out of the post-war party.
But something flipped their attitude, and it's pretty clear to me that the French will support the action, and may even be trying to part of the combat operation.
The reversal is rather stunning.