In reply to chev1n:
Hi Chev,
The camp site near Milly la Foret is called La Musardière (+33 1 64 98 91 91 ) they speak a reasonable english when you want something and even better English when they want some (ie money). However depending when you go you will find others here who are also boulderers and usually happy to share information as well as good facilities (showers, washing up, pool, pay phone).
There are other campsites but they tend not to be near to the more popular areas. If you can get hold of a guide that would make things a lot easier. The Jingo 'Wibbly' Wobbly guide is probably the best general one (www.jingowobbly.com/fom/fom-main.html), but I guess that depends on whether you can translate French or not.
Flying to Paris is your best bet, gathered you have worked that out already, you can then get a train (for free if you're feeling skint and willing to risk it for a biscuit) to Fontainebleau Avon which is the train station in Font. From here, there are buses or taxis. I'm not much of an expert on theese but I know it cost two lads somewhere around 20 euro to get from Font to the afore mentioned campsite. You could probably hitch pretty easily if you knew where you were going exactly, or you were lucky enough to find someone who spoke English. You can then hire bikes from the campsite or walk places pretty easily. But, I'm guessing you would like to explore a lot in your short time so a bike is probably better. Can't remember prices exactly but I can remember thinking it as being reasonable.
Flying you can take pretty much anything in hold luggage(luggage that goes in the bottom of the plane). Depending on which company you fly with you could have anything from 15kg to 30kg (I think) of allowance. But if you are really worried, you can get screw on gas stoves in Milly (which is cyclable from the campsite)in the hardware store next to the supermarket there. However, it is expensive and would save you time and effort just to buy it in England. Flying a pad on a plane, I have no experience of this though, I reckon it would be expensive, especially on the budget airlines.
October is the best time of year to go.
Have fun! Hope this has been helpful!