Hope you have got it all working now.

Nope! And my housemate is complaining since he's paying for broadband and only my computer can access the net! Pressure! ;)

As you are using dhclient something like

dhclient -i eth0

dhclient won't work until I compile config_packet=yes into my kernel. Sadly, make-kpkg exits with errors (unresolved symbols) even after a make clean and make mrproper. In fact, I deleted /usr/src/linux and untarred it and tried again, with the same errors, which is odd to say the least!

I'll get the kernel recompiled and then try again. did you turn off the set top box for a while before attaching it to the network?

It still doesn't explain why neither windows nor linux couldn't get external sources via the ipcop box... oh well!