For a few days, our only internet access was throught wireless network with the Nokia 770. I tried with the laptop but the prism54 card I'm using didn't get any signal while the Nokia 770 could.

Could we turn the Nokia 770 into an USB to Wifi adapter? I think it is possible. We have almost all the bricks. We just need to write a CDCEther driver for the USB slave (relatively trivial, I have done that in the past for the freebox) and bridge that ethernet interface to the wifi driver. And all the wifi specific configuration be handled by the UI in Maemo. Linux has a CDCEther driver built-in.