It seems that the specific drivers required for your NICs (Broadcom NetExtreme II according to google...) were removed from the Debian kernel some time ago (because of licencing restrictions...)

The firmware package required is firmware-bnx2. For TKL v12 it can be downloaded from here: http://packages.debian.org/squeeze/firmware-bnx2 or a later version here: http://packages.debian.org/squeeze-backports/firmware-bnx2 (to download scroll down to the Download section and click 'all' under architecture then select your mirror. Once downloaded, copy it to a USB stick (preferably formatted with FAT of some description).

Before you plug it into your server run

fdisk -l

Then plug the USB in and run that command again. There should be one additional line (something like /dev/sdb or similar). Assuming that it is sdb (substitue sdc1 or sdd1 or whatever it is if it isn't sdb...) mount it

mount /dev/sdb1 /mnt

Then install the deb

cd /mnt
dpkg -i firmware-bnx2_0.28+squeeze1_all.deb

(obviously substitute the name of the deb if you use the later backport version, etc also note that you can use <Tab> to auto complete the filename after you have typed the first few chars)

Now reboot

reboot

And you should now be good to go! :)