The French foreign minister is now saying the world should prepare for war with Iran. Considering their stance on other conflicts why now?

Partly because they have changed president since the Iraq invasion - Sarkozy is politically closer to Bush or Blair than Chirac was. Partly because Iran gaining nuclear weapons could actually be a threat to the entire region and feasibly Europe, as opposed to Saddam and his non-existent WMDs, who was of no threat to anyone outside Iraq.

It is unusual for the French to take a more aggresive stance and thats all well and good now but if conflict with Iran did arise they would be extremely quick to back out and completely readdress their position so it is just the current politicians who are in favour of action and as soon as that changes so will their stance.