Discovered a few weeks ago that an AT&T U-Verse cable box would work as a HPNA to Ethernet bridge. With the cable signal coming through the coax line to the STB the ethernet jack on the back was live and allowed me to connect an Apple Airport and get the wireless signal much stronger throughout the house.
Found a flaw this morning though when the STB restarted to get an update. It looks like if both the coax and ethernet jack are plugged in the box tries to connect via cat5 first, which meant it was trying to get an IP from the AirPort. Obviously not a good way of doing things since the AirPort is supposed to connect back through the U-Verse box to get out to the rest of the network.
Several reboots and red X screens later, I tried unhooking the ethernet cable and restarting the STB. Worked like a champ. Guess that’s just something to remember next time I have to restart the cable box.