Air France has indeed signed a firm order for eight Airbus Industrie A330-200s with options for a further five. They will replace their Boeing 767's. Air France has indeed got 777 and they seem to be very happy with these aircraft. They are named to be lauch customer for the 777-300ER.
Air France currently operates its 5 767-300ER from CDG to :
-BOS (2 daily flights)
-ORD (the first flight)
I think that the 777s will replace the 767s on these routes, because AF aims to grow on the trans-atlantic market, thanks to its alliance with Delta.
Don't forget that the 10 A310s will also leave the fleet in the next 5 years. That's why I think that AF will use the A330 to the markets served by the 310s. (Africa and Middle East).
The A330-200s will offer 219 seats (probably in a triclass configuration), whereas the A310s have 166/177 seats and the 767s 210s.
The 777-200ER and A330-200 are really aimed at two different market slots at Air France.
As Louis said, the 777 should be the backbone of the US operations. They are already operating JFK, LAX, IAD, ATL.
I the 777 should replace the 767s and 747-200s there, with the A310s replaced by the A330-200.
The 777 has very good results in the Air France's fleet. However it would be much to large for some African and Middle-Eastern routes. And it was even an issue when they had to chose between the 767-400ER or the A330-200. The former was smaller, and thus maybe better for these thin routes.
Also it wouldn't have been interesting for Air France to fly only A330s and no 777s on the North Atlantic. The A330-200 would have been too narrow for the US routes, and the A330-300 would have lacked range for the Asian routes (and this aircraft is also smaller than the 777-200ER).