I don't know Freeserve/Wanadoo's wireless livebox kit and its associated settings.
But to help others who do know, please also post the make and specific models of the wireless kit you have;
> Inventel USB (wireless?) adapter.
> Linksys Laptop Card.
11Mbps sounds like 802.11b speed (12Mbps) ~ have you set the Linksys laptop card to run on 802.11b ratherm then 802.11g (54Mbps)?