€12/month for 'unlimited' web + 10 MB mail access.
Access may be terminated or capped after 500 MB download for the rest of the month, but it is reported, that this limit is not enforced (as of September 2008). It is not possible to renew this plan within the that same month to restore access.
Terms and conditions say the option is only for handset-based access, however it could be used flawlessly from a computer in September 2008.

• A Mobicarte prepaid SIM can be bought without a phone in Orange shops for 30 euros or for less than € 10 at the French branch of that big auction site. The initial credit is € 4,50 for calls and 100kb for surfing.
• Coupons for recharging can be bought at post offices, supermarkets and of course orange shops.
  

• To activate the 5 MB option, additional credit (e.g. 10 euros) has to be bought. Current balance can be checked by typing #123# + dial button.

• To activate one of the options described above, call '220' and select 'Découverte Multimedia' or 'Internet Max' from the 'Multimedia Menu'. The price for the option will be immediately taken from the prepaid account.

• It's also possible to activate one of the options via the #123# USSD dialogue. When the current credit is shown, answer with '00' to go to the main menu and go to 'gerer vos option' from there. Here's a picture of how the screen looks like in that menu:

• Press #123# to activate to the mobicard menu.
• Select 3 for the menu
• Select 2 for "Recharger"
• Select 1 "par recharge mobicarte"
• Enter your 14 digit card code.

• Again, select #123# to activate the mobicard menu
• Select 3 for the menu
• Select 3, Vos bons plans
• Select 4, Votre multimedia
• Select 3, Option Internet Max
• Acknowledge the following general terms and conditions with 1 (several times)

• APN: orange (tried with 'decouverte multimedia' option but should work for 'Internet max' as well)
• Username: orange (might not be required)
• Password: orange (might not be required)