Need help - France SIM

[Tally Ho! Travel]

I'm new here (great site by the way), but I've done some searching and don't see an answer to my question in any old threads.

I am about to leave for France for a 6 weeks stay. I have a cellphone I bought at Orange a couple of years ago, but my number has expired. Does this mean I need to buy a new SIM? Specifically, where can I buy the cards? Is there possibly a kiosque at CDG? I'd like to be able to make calls as soon after I land as possible. Is it necessary to buy an Orange SIM or can I purchase any brand? How do I determine which one provides the best rate? My son will be traveling with me and bringing his unlocked quadband, so we will also need a SIM for his phone.

If it helps to know, I need to be able to make calls to numbers in France and to the US, and to receive calls from numbers in France and the US (all at the cheapest rates, of course! ).

Thanks for any assistance you can give me. This is all new to me.