I would start by contacting the owner of the IP address, in this case Wanadoo, a French Internet Service Provider (ISP). Check the Wanadoo web site for abuse contacts. If not found, send a polite letter to abuse@wanadoo.fr explaining the issue, and attach whatever logs/trace info you have.

If you can find a copy of their Terms & Conditions on the site, a quote from a section that directly address attempts at breaking into machines, would be useful.

Ask that you be contacted with information about what action they plan to take. Do not ask for the identity of the intruder. They will - and should not - devulge that kind of information to a 3rd party, but you are entitled to know what/if they will do about it.

If you do not get a response, you can either write again, perhaps send a fax, or call the switchboard and ask to talk with the helpdesk manager.

Alternatively, instead of going after an un-cooperative ISP, try some of the others that appear in your logs. Once you succesfully manage to shut down an offender, you can cite/quote the case in the letter to abuse@unresponsive.isp.

Best of luck,
MiniMax