So normally you don't have to do any configuration on things you plug into your wired network?

It sounds like it's not picking up a DNS server properly. I would check the configuration on the cable box for that entry. If it's not auto-filling (via DHCP), you can use Google's DNS servers at 8.8.8.8 and 8.8.4.4.

I am the Doctor, and THIS... is my SPOON!