Copy/paste your xterm window here. (if you are attempting to edit /etc/network/interfaces and it gives you the message "permission denied" then you aren't root!)
N900 USB network configuration If you are going to use windows as your host, the configuration needed on your N900 are a little different, so skip directly to the "Starting USB network mode with Windows" Part. There is a default USB network interface configuration on Nokia N900. In the file /etc/network/interfaces, you should see a section which looks like this: auto usb0 iface usb0 inet static address 192.168.2.15 netmask 255.255.255.0 gateway 192.168.2.14
auto usb0 iface usb0 inet static address 192.168.2.15 netmask 255.255.255.0 gateway 192.168.2.14