Regarding your theory: I think it is possible, although a betrayal of such magnitude would be grounds for war and I hope it isn't true.
Something is driving this, and a desire for EU dominance just doesn't ring true. Neither do oil contracts, trading partnerships, or French's desire for greatness.
A nuke is a possibility, although the French government could blame it on a rogue scientist or corporation.
I am getting the heeby-jeebies thinking about this.
Even the French aren't that crazy. They may have helped the terrorists by selling prescribed goods, but I find it hard to imagine that they would be the driving force in a planned terrorist attack on the US. They could sell a small nuke if they wanted to play that game. They've been arresting terrorists and sharing intelligence, and if they'd been on the other side, they wouldn't be doing that for fear of what would turn up.
So, I doubt their involvement in 9-11, but at this point I think Chirac wishes he had thought of it.