Add non-free firmware drivers

From Andreida

if you get for example the message:

Possible missing firmware /lib/firmware/rtl_nic/rtl8168d-2.fw for module r8169

/etc/apt/sources.list add

deb http://ftp.uk.debian.org/debian/ squeeze main non-free

apt-get install firmware-realtek
dpkg-reconfigure initramfs-tools