When we did our unsupported bike trip (that is, on our own), we needed to transport our bicycles to the starting point of our bike trip, Chateaudun. (It is generally a bad idea to bike out of the airport--the roads are invariably very crowded and NO FUN to bike on.) We found a company that was able to provide a van to carry four of us and our four bikes, and it worked perfectly.
The transportation was provided by Dunois Voyages, which has offices in Orleans, Chateaudun, Blois, and Joue les Tours. The phone number is Chateaudun (which was our dropoff and pickup point) is 37.44.63.00, fax 18.104.22.168. The cost was 3980F, which is a lot of money, but not too bad divided by four--and considering the distance (about a 2 hour drive) and how flawlessly it worked.
It is, of course, possible to transport bicycles on the trains in France, but only on certain trains--and there is no guarantee that the bikes will be on the same train as the people. We were unwilling to take the chance that we would have to wait around for our bikes to arrive, and considered it well worth the extra expense to have foolproof transportation for us and them.