Run a network lead and just slap a raspberry pi on the back. If it is only going to be used for a rotating webpage the pi can more than handle it whilst being silent.
I use a R Pi for a home entertainment center. The video utput is HDMI and manages to run XBMC just fine. I can watch HD video anywhere I can plug in a network cable :D
For watching live TV there is a free plugin for xbmc that allows you to watch the freeview / cable channels streamed online. - thought I would add that since you mentioned cable tv.
