Depending on your cable provider you will get sd channels with just cable to tv. Usually HD channels need a hd box, assuming the tv is 720p or 1080i. you will get HD channels. If you don't want to pay for cable, an over the air HD antenna will get you digital/HD channels for free depending where you live.
TV - Panasonic 55GT50Main Speakers - Klipsch Gallery G28'sCenter Channel- Klipsch RC-52Sub - Klipsch Sub 12Surrounds - Klipsch RS-52 II (new)Bluray/Game - HTPC/PS3Receiver - Onkyo RC-360HTPC - Intel Core i3, HDMI,Windows 7,XBMC,Bluray,3 TB,wireless WMC keyboardVideo processor - Darbee