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