The basics of IPTV aren't that hard to understand.
You're just taking an analog (or digital in some cases) signal and converting it to "Internet Protocol", the same type transmission used to bring you web pages and email and whatnot. The medium you would usually seen employed to bring a full scale IPTV service offering would be fiber optic cables. You can push IPTV over copper, but it would become maxed out after only a few channel requests from several customers (even more impacted by HDTV). You would have a special set top box for your TV that would decode the packets and display the video on your tv just like regular cable.
If you're looking for very technical and specific information about the whole process read this: