My understanding of the France Telecom/Orange deal is that you are limited to the Orange mobile portal (the equivalent to 'Orange World' in the UK) and are not allowed to use your phone as a modem. The small quantity of data included in the plan would soon be used up if you did in any case. Basically it's designed for internet access on your phone.
Better would be the sim cards available from the Auchan supermarket chain, which
are designed for full laptop access. Although not cheap by UK standards, they appear to be a much better deal than anything else available in France. See
here.
The €29.90 card seems to include 50MB, subject to a maximum 5 hours connection time. A €25 top-up from one of the shops gets you the same, and must be used within 45 days. Higher (and slightly better) value top-ups can only be bought via the mobile portal. This might mean needing a french debit card or address. I hope to find out when I get to France next week.