Connecting via usb was a stupid thing with the old FW,

now nokia has (silently ) removed the module g_ether from the standard kernel and has putted the module g_nokia in his place.

Unluckily the usb lan that come from the use of g_nokia is not recognized at all from windows.

So, to get the usb networking back you have to.

#1 download and install the package mad developer which provide the module g_ether

#2 unload (rmmod) the conflicting modules (g_nokia and g_file_storage)

#3 modprobe the module g_ether

#4 bring up and configure the usb interface.

#5 install the drivers for windows

You can use the mad developer gui to accomplish the above steps

then you can easily use the windows ICS to share the connection to the n900.