It is very difficult to get a local french SIM card with data anyhow. It's just so different from here. Unless you have an iPhone or BB, the french appear to think you don't want or need data use and it's expensive where it exists at all.
I have a leClerc mobile as the credit lasts a year but they don't do data. Some others only do WAP.
Orange (who are a nightmare to deal with) have limited access to the web via the Orange portal only. Have a look here under 'combine ca coute' (how much does it cost)
http://www.orange.fr/bin/frame.cgi?u...ultimedia.html
Many french websites are a nightmare to navigate, completely user unfriendly. All my french mates have a 2 hour per month pay monthly for some exorbitant amount that we'd get about 900 mins and unlimited texts and data for in the UK. They only use their mobiles for texts.
As for using your UK mobile for data in France, it's eye wateringly expensive. You'd be better finding an internet cafe. Even wifi hotspots are few and far between outside of the big cities - try macdonalds if there is one as they often have them. HTH
PS you will need a french mate to lend you their address to get a local SIM. You buy it instore and they would have to come with you and buy it