Download the package from a pc connected to the internet, and transfer it to XBMC using a USB drive. After it's connected, your USB drive will be located in the /media directory. I'm not sure if you can install the package from the USB so copy the file to /var/cache/apt/archives. That's where all the packages from the updates are located.
sudo apt-get install lshw
If any packages are missing, go back and download them. After that, check out that How To I mentioned earlier.
Not sure what your /etc/network/interfaces looks like, but something might not be commented out correctly. It should look like this:
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
iface lo inet loopback
# The primary network interface
iface eth0 inet dhcp