After rummaging around I see that it is a Samsung SMT-C7100 - a Tivo box in some places is described as a Cisco router.
It doesn't seem to be looking for an IP address, so I guess it must establish a cable connection with the ISP. I did see some references to Linux on the hard disk when I took it out, but I don't know if it's possible to boot it up from USB. I can't work out what processor it uses, but the specs say it uses Tivo middleware.
I wonder if it uses u-Boot to boot in which case I might be able to connect up a serial cable...